:root {
  --bg: #f7f8fb;
  --surface: #ffffff;
  --surface-soft: #eef7f5;
  --text: #18202f;
  --muted: #647084;
  --line: #dfe5ec;
  --teal: #0d9488;
  --blue: #2563eb;
  --rose: #e14d5a;
  --amber: #c47f12;
  --shadow: 0 18px 50px rgba(24, 32, 47, 0.08);
  color-scheme: light;
}

* {
  box-sizing: border-box;
}

html {
  scroll-behavior: smooth;
}

body {
  margin: 0;
  background: var(--bg);
  color: var(--text);
  font-family: "LXGW WenKai", "Microsoft YaHei", ui-sans-serif, system-ui, -apple-system, BlinkMacSystemFont, "Segoe UI", sans-serif;
  line-height: 1.72;
}

.sr-only {
  height: 1px;
  margin: -1px;
  overflow: hidden;
  padding: 0;
  position: absolute;
  width: 1px;
}

a {
  color: var(--blue);
  text-decoration: none;
}

a:hover {
  text-decoration: underline;
}

.site-shell {
  min-height: 100vh;
  position: relative;
  z-index: 1;
}

.home-page .site-header {
  display: none;
}

.home-page .main-grid {
  padding-top: 42px;
}

.home-hero {
  align-items: center;
  background:
    linear-gradient(180deg, rgba(5, 12, 30, 0.08), rgba(7, 11, 28, 0.18)),
    url("hero-bg.png") center 70% / cover no-repeat;
  color: #fff;
  display: flex;
  justify-content: center;
  min-height: 100vh;
  overflow: hidden;
  position: relative;
  text-align: center;
}

.home-hero::after {
  background: rgba(5, 12, 30, 0.1);
  content: "";
  inset: 0;
  pointer-events: none;
  position: absolute;
  transition: background 0.3s ease;
}

.theme-dim .home-hero::after,
.drawer-open .home-hero::after {
  background: rgba(5, 12, 30, 0.42);
}

.hero-content {
  position: relative;
  text-shadow: 0 6px 18px rgba(0, 0, 0, 0.38);
  z-index: 1;
}

.hero-content h1 {
  font-family: "Brush Script MT", "Segoe Script", "LXGW WenKai", cursive;
  font-size: clamp(3rem, 8vw, 5.8rem);
  letter-spacing: 0;
  line-height: 1;
  margin: 0;
}

.hero-content p {
  font-family: "Segoe Script", "LXGW WenKai", cursive;
  font-size: clamp(1rem, 2vw, 1.35rem);
  margin: 18px 0 0;
  opacity: 0.9;
}

.scroll-down {
  bottom: 6vh;
  color: rgba(255, 255, 255, 0.78);
  font-size: 4.2rem;
  left: 50%;
  line-height: 1;
  position: absolute;
  text-shadow: 0 4px 12px rgba(0, 0, 0, 0.35);
  transform: translateX(-50%);
  z-index: 1;
}

.scroll-down:hover {
  color: #fff;
  text-decoration: none;
}

.menu-button {
  align-items: center;
  background: rgba(17, 24, 39, 0.22);
  border: 1px solid rgba(255, 255, 255, 0.55);
  border-radius: 4px;
  color: #fff;
  display: inline-flex;
  font: 600 0.95rem/1 ui-monospace, SFMono-Regular, Consolas, monospace;
  gap: 10px;
  height: 40px;
  left: 28px;
  letter-spacing: 0.04em;
  padding: 0 16px;
  position: fixed;
  top: 24px;
  z-index: 50;
}

.menu-button:hover {
  background: rgba(17, 24, 39, 0.42);
}

.theme-switch {
  background: rgba(82, 166, 191, 0.78);
  border: 2px solid rgba(30, 45, 80, 0.42);
  border-radius: 999px;
  box-shadow: 0 15px 10px -10px rgba(0, 0, 0, 0.28);
  height: 34px;
  overflow: hidden;
  position: fixed;
  right: 28px;
  top: 30px;
  width: 86px;
  z-index: 50;
}

.theme-switch-orb {
  background: #ffdf61;
  border: 2px solid #d9b31c;
  border-radius: 50%;
  height: 24px;
  position: absolute;
  right: 5px;
  top: 3px;
  transition: transform 0.3s ease;
  width: 24px;
}

.theme-switch-sky::before,
.theme-switch-sky::after {
  background: rgba(255, 255, 255, 0.62);
  border-radius: 99px;
  content: "";
  height: 3px;
  position: absolute;
  right: 34px;
  top: 13px;
  width: 28px;
}

.theme-switch-sky::after {
  right: 42px;
  top: 19px;
  width: 18px;
}

.theme-dim .theme-switch {
  background: rgba(50, 65, 100, 0.88);
}

.theme-dim .theme-switch-orb {
  background: #f0e1a5;
  border-color: #ccc091;
  transform: translateX(-50px);
}

.drawer-backdrop {
  background: rgba(0, 0, 0, 0.32);
  inset: 0;
  position: fixed;
  z-index: 55;
}

.site-drawer {
  background:
    linear-gradient(rgba(14, 18, 27, 0.9), rgba(14, 18, 27, 0.9)),
    url("hero-bg.png") left center / cover no-repeat;
  border-right: 1px solid rgba(255, 255, 255, 0.12);
  bottom: 0;
  color: rgba(255, 255, 255, 0.86);
  left: 0;
  max-width: calc(100vw - 36px);
  overflow-y: auto;
  padding: 18px 18px 70px;
  position: fixed;
  top: 0;
  transform: translateX(-104%);
  transition: transform 0.28s ease;
  width: 344px;
  z-index: 60;
}

.drawer-open .site-drawer {
  transform: translateX(0);
}

.drawer-title {
  align-items: center;
  border-bottom: 1px solid rgba(255, 255, 255, 0.1);
  display: flex;
  font-style: italic;
  gap: 12px;
  justify-content: space-between;
  padding-bottom: 14px;
}

.drawer-title button {
  background: transparent;
  border: 0;
  color: rgba(255, 255, 255, 0.62);
  font-size: 1.6rem;
}

.drawer-profile {
  align-items: center;
  display: flex;
  gap: 18px;
  padding: 24px 0;
}

.drawer-profile img {
  border: 3px solid rgba(255, 255, 255, 0.76);
  border-radius: 50%;
  height: 88px;
  object-fit: cover;
  width: 88px;
}

.drawer-stats {
  border-bottom: 1px solid rgba(255, 255, 255, 0.1);
  border-top: 1px solid rgba(255, 255, 255, 0.1);
  color: rgba(255, 255, 255, 0.7);
  padding: 12px 0;
}

.drawer-search {
  align-items: center;
  background: rgba(255, 255, 255, 0.1);
  border-radius: 4px;
  display: flex;
  gap: 8px;
  margin: 22px 0;
  padding: 0 12px;
}

.drawer-search input {
  background: transparent;
  border: 0;
  color: #fff;
  flex: 1;
  font: inherit;
  min-height: 42px;
  outline: 0;
}

.drawer-search input::placeholder {
  color: rgba(255, 255, 255, 0.42);
}

.drawer-nav {
  display: grid;
  gap: 10px;
}

.drawer-nav a {
  align-items: center;
  color: rgba(255, 255, 255, 0.86);
  display: grid;
  gap: 14px;
  grid-template-columns: 34px 1fr auto;
}

.drawer-nav a:hover {
  color: #fff;
  text-decoration: none;
}

.drawer-nav span {
  align-items: center;
  background: rgba(255, 255, 255, 0.12);
  border-radius: 4px;
  display: inline-flex;
  height: 34px;
  justify-content: center;
}

.drawer-nav strong {
  border-bottom: 1px dotted rgba(255, 255, 255, 0.18);
  font-weight: 500;
  padding-bottom: 4px;
}

.drawer-nav em {
  color: rgba(255, 255, 255, 0.48);
  font-style: normal;
}

.drawer-calendar {
  background: rgba(8, 12, 20, 0.34);
  margin: 28px -12px 0;
  padding: 12px;
}

.calendar-head {
  align-items: center;
  display: flex;
  justify-content: space-between;
  margin-bottom: 10px;
}

.calendar-grid {
  display: grid;
  gap: 8px;
  grid-template-columns: repeat(7, 1fr);
  text-align: center;
}

.calendar-grid span {
  color: rgba(255, 255, 255, 0.42);
  min-height: 22px;
}

.calendar-grid .calendar-today {
  color: #fff;
  font-weight: 700;
}

.drawer-bottom {
  align-items: center;
  background: rgba(6, 9, 16, 0.62);
  bottom: 0;
  display: grid;
  grid-template-columns: repeat(4, 1fr);
  left: 0;
  min-height: 44px;
  position: fixed;
  width: 344px;
}

.drawer-bottom a {
  color: rgba(255, 255, 255, 0.86);
  font-size: 0.9rem;
  text-align: center;
}

.site-header {
  border-bottom: 1px solid var(--line);
  background: rgba(255, 255, 255, 0.88);
  backdrop-filter: blur(14px);
  position: sticky;
  top: 0;
  z-index: 10;
}

.header-inner,
.main-grid,
.footer-inner {
  width: min(1120px, calc(100% - 32px));
  margin: 0 auto;
}

.header-inner {
  min-height: 72px;
  display: flex;
  align-items: center;
  justify-content: space-between;
  gap: 18px;
}

.brand {
  display: inline-flex;
  align-items: center;
  gap: 12px;
  min-width: 0;
  color: var(--text);
}

.brand img {
  width: 44px;
  height: 44px;
  border-radius: 8px;
  box-shadow: var(--shadow);
}

.brand strong {
  display: block;
  font-size: 1.05rem;
  line-height: 1.15;
}

.brand span {
  display: block;
  color: var(--muted);
  font-size: 0.82rem;
  line-height: 1.35;
}

.nav-links {
  display: flex;
  align-items: center;
  gap: 14px;
  color: var(--muted);
  font-size: 0.94rem;
  white-space: nowrap;
}

.main-grid {
  display: grid;
  grid-template-columns: minmax(0, 1fr) 320px;
  gap: 28px;
  padding: 34px 0 56px;
}

.intro {
  display: grid;
  grid-template-columns: minmax(0, 1fr) 250px;
  align-items: center;
  gap: 22px;
  padding: 28px;
  background: var(--surface);
  border: 1px solid var(--line);
  border-radius: 8px;
  box-shadow: var(--shadow);
}

.intro h1 {
  margin: 0 0 12px;
  font-size: clamp(2rem, 5vw, 4.6rem);
  line-height: 1;
  letter-spacing: 0;
}

.typewriter-cursor::after {
  animation: cursorBlink 0.8s infinite;
  content: "|";
  margin-left: 4px;
}

.intro p {
  margin: 0;
  color: var(--muted);
  max-width: 56ch;
}

.intro img {
  width: 100%;
  border-radius: 8px;
  border: 1px solid var(--line);
}

.toolbar {
  margin: 24px 0 16px;
  display: flex;
  align-items: center;
  gap: 12px;
}

.search-input {
  width: 100%;
  min-height: 44px;
  border: 1px solid var(--line);
  border-radius: 8px;
  background: var(--surface);
  color: var(--text);
  padding: 0 14px;
  font: inherit;
}

.post-list {
  display: grid;
  gap: 14px;
}

.post-card {
  display: block;
  padding: 22px;
  background: var(--surface);
  border: 1px solid var(--line);
  border-radius: 8px;
  color: var(--text);
  box-shadow: 0 10px 28px rgba(24, 32, 47, 0.05);
}

.post-card:hover {
  border-color: rgba(13, 148, 136, 0.44);
  text-decoration: none;
}

.post-card h2 {
  margin: 0 0 8px;
  font-size: 1.35rem;
  line-height: 1.28;
}

.post-card p {
  margin: 0 0 14px;
  color: var(--muted);
}

.meta {
  display: flex;
  flex-wrap: wrap;
  gap: 8px 12px;
  color: var(--muted);
  font-size: 0.88rem;
}

.tag {
  color: var(--teal);
  background: var(--surface-soft);
  border-radius: 999px;
  padding: 2px 9px;
}

.side-panel {
  display: grid;
  gap: 14px;
  align-content: start;
}

.panel {
  background: var(--surface);
  border: 1px solid var(--line);
  border-radius: 8px;
  padding: 20px;
}

.panel h2 {
  margin: 0 0 10px;
  font-size: 1rem;
}

.panel p,
.panel li {
  color: var(--muted);
  font-size: 0.94rem;
}

.panel ul {
  margin: 0;
  padding-left: 18px;
}

.article-layout {
  align-items: start;
  display: grid;
  gap: 24px;
  grid-template-columns: minmax(0, 820px) 230px;
  justify-content: center;
  padding: 34px 24px 56px;
}

.article {
  max-width: 820px;
  margin: 0;
  background: rgba(255, 255, 255, 0.95);
  border: 1px solid var(--line);
  border-radius: 8px;
  padding: clamp(24px, 5vw, 54px);
  box-shadow: var(--shadow);
  font-size: 16px;
  line-height: 1.9;
}

.article-header {
  border-bottom: 1px solid var(--line);
  margin-bottom: 30px;
  padding-bottom: 22px;
}

.article-actions {
  display: flex;
  flex-wrap: wrap;
  gap: 10px;
  margin-top: 18px;
}

.pdf-download,
.quiz-challenge-start {
  align-items: center;
  background: var(--teal);
  border: 1px solid rgba(13, 148, 136, 0.2);
  border-radius: 8px;
  color: #fff;
  cursor: pointer;
  display: inline-flex;
  font: inherit;
  font-weight: 700;
  justify-content: center;
  min-height: 40px;
  padding: 0 14px;
}

.pdf-download:hover,
.quiz-challenge-start:hover {
  background: #0f766e;
  color: #fff;
  text-decoration: none;
}

.quiz-challenge-start {
  background: var(--blue);
  border-color: rgba(37, 99, 235, 0.22);
}

.quiz-challenge-start:hover {
  background: #1d4ed8;
}

.article-toc {
  position: sticky;
  top: 92px;
}

.article-toc-inner {
  background: rgba(255, 255, 255, 0.95);
  border: 1px solid var(--line);
  border-radius: 8px;
  box-shadow: 0 10px 28px rgba(24, 32, 47, 0.05);
  display: grid;
  gap: 14px;
  grid-template-rows: auto auto minmax(0, 1fr);
  max-height: calc(100vh - 116px);
  min-height: 0;
  padding: 16px;
}

.article-toc strong {
  font-size: 0.95rem;
}

.article-toc nav {
  display: grid;
  gap: 6px;
  max-height: 100%;
  min-height: 0;
  overflow-y: auto;
  overscroll-behavior: contain;
  padding-right: 4px;
  scrollbar-width: thin;
}

.article-toc nav a {
  border-left: 2px solid transparent;
  color: var(--muted);
  font-size: 0.9rem;
  line-height: 1.35;
  padding: 5px 0 5px 10px;
}

.article-toc nav a:hover {
  border-left-color: var(--teal);
  color: var(--text);
  text-decoration: none;
}

.article-toc .toc-level-3 {
  padding-left: 22px;
}

.article-toc .toc-level-4 {
  padding-left: 34px;
}

.part-list {
  display: grid;
  gap: 8px;
  list-style: decimal;
  margin: 10px 0 18px;
  padding-left: 1.45em;
}

.part-list li {
  padding-left: 4px;
}

.qa-card .part-list {
  list-style-type: decimal;
}

.blank-line {
  border-bottom: 1px solid currentColor;
  display: inline-block;
  min-width: 8em;
  transform: translateY(-0.15em);
}

.blank-space {
  display: inline-block;
  min-width: 1.5em;
}

.article h1 {
  margin: 0 0 14px;
  font-size: clamp(2rem, 6vw, 3.6rem);
  line-height: 1.08;
  letter-spacing: 0;
}

.article h2,
.article h3,
.article h4 {
  font-weight: 700;
  line-height: 1.25;
  margin: 2.1em 0 0.7em;
}

.article p {
  margin: 1em 0;
}

.article ol,
.article ul {
  padding-left: 1.35rem;
}

.article li {
  margin: 0.3em 0;
}

.article img {
  max-width: 100%;
  border-radius: 12px;
  border: 1px solid var(--line);
}

.abstract,
.math-box,
.theorem,
.proof,
blockquote,
.knowledge-block {
  border-left: 4px solid #409eff;
  background: rgba(64, 158, 255, 0.08);
  margin: 22px 0;
  padding: 14px 18px;
  border-radius: 0 8px 8px 0;
}

.knowledge-block {
  background: rgba(37, 99, 235, 0.07);
  border-left-color: var(--blue);
}

.center-block {
  text-align: center;
}

.center-block figure {
  margin-left: auto;
  margin-right: auto;
}

.theorem {
  border-left-color: var(--rose);
  background: #fff5f6;
}

.proof {
  border-left-color: var(--amber);
  background: #fff9ed;
}

.qa-card {
  background: #fff;
  border: 1px solid rgba(13, 148, 136, 0.18);
  border-radius: 8px;
  box-shadow: 0 10px 28px rgba(24, 32, 47, 0.05);
  margin: 18px 0;
  padding: 16px 18px;
  position: relative;
}

.question-title {
  color: var(--text);
  font-weight: 700;
  margin: 0 0 10px;
}

.qa-card ul {
  margin: 8px 0 0;
}

.qa-card ol {
  list-style-type: decimal;
  margin: 8px 0 0;
}

.qa-card .option-list {
  list-style-type: upper-alpha;
}

.qa-card.is-interactive li[data-option] {
  border: 1px solid transparent;
  border-radius: 8px;
  cursor: pointer;
  list-style-position: inside;
  padding: 7px 10px;
  transition: background 0.16s ease, border-color 0.16s ease, color 0.16s ease;
}

.qa-card.is-interactive li[data-option]:hover,
.qa-card.is-interactive li[data-option]:focus {
  background: rgba(37, 99, 235, 0.07);
  border-color: rgba(37, 99, 235, 0.2);
  outline: none;
}

.qa-card li.is-selected {
  background: rgba(37, 99, 235, 0.1);
  border-color: rgba(37, 99, 235, 0.32);
}

.qa-card li.is-correct-option {
  background: rgba(13, 148, 136, 0.12);
  border-color: rgba(13, 148, 136, 0.42);
  color: #0f766e;
}

.qa-card li.is-wrong-option {
  background: rgba(225, 77, 90, 0.1);
  border-color: rgba(225, 77, 90, 0.38);
  color: #b42332;
}

.quiz-controls {
  align-items: center;
  display: flex;
  flex-wrap: wrap;
  gap: 10px;
  margin-top: 14px;
}

.quiz-button {
  background: var(--text);
  border: 1px solid rgba(24, 32, 47, 0.14);
  border-radius: 8px;
  color: #fff;
  cursor: pointer;
  font: inherit;
  font-weight: 700;
  min-height: 34px;
  padding: 0 12px;
}

.quiz-button:hover {
  background: #273247;
}

.quiz-button-secondary {
  background: #fff;
  color: var(--text);
}

.quiz-button-secondary:hover {
  background: #f8fafc;
}

.quiz-status {
  color: var(--muted);
  font-weight: 700;
  margin: 0;
}

.quiz-correct .quiz-status {
  color: #0f766e;
}

.quiz-wrong .quiz-status {
  color: #b42332;
}

.answer-line,
.explanation-line {
  background: rgba(13, 148, 136, 0.08);
  border-radius: 8px;
  color: #0f766e;
  display: block;
  margin: -8px 0 20px;
  padding: 8px 12px;
}

.answer-line > strong,
.explanation-line > strong {
  display: block;
  margin-bottom: 4px;
}

.answer-line p,
.explanation-line p {
  margin: 0.55em 0;
}

.answer-line[hidden],
.explanation-line[hidden] {
  display: none;
}

.knowledge-card {
  background:
    linear-gradient(180deg, rgba(255, 255, 255, 0.96), rgba(238, 247, 245, 0.96));
  border: 1px solid rgba(13, 148, 136, 0.2);
  border-radius: 8px;
  box-shadow: 0 18px 44px rgba(24, 32, 47, 0.1);
  color: var(--text);
  padding: 14px 16px;
  position: relative;
}

.knowledge-card span {
  color: var(--teal);
  display: block;
  font-size: 0.78rem;
  font-weight: 700;
  letter-spacing: 0.08em;
  margin-bottom: 6px;
}

.knowledge-card strong {
  display: block;
  font-size: 1rem;
  line-height: 1.35;
  margin-bottom: 8px;
}

.knowledge-card p {
  color: var(--muted);
  font-size: 0.9rem;
  line-height: 1.6;
  margin: 0;
}

.knowledge-card-body {
  color: var(--muted);
  display: grid;
  font-size: 0.9rem;
  gap: 8px;
  line-height: 1.6;
  max-height: min(540px, 70vh);
  overflow-y: auto;
  padding-right: 4px;
  scrollbar-width: thin;
}

.knowledge-card-body p {
  margin: 0;
}

.knowledge-card-body .math-box {
  margin: 0;
  overflow-x: auto;
  padding: 10px 12px;
}

.knowledge-card-body ol,
.knowledge-card-body ul {
  margin: 0;
  padding-left: 1.2rem;
}

@media (min-width: 1700px) {
  .knowledge-card {
    left: calc(100% + 300px);
    position: absolute;
    top: 20px;
    width: 250px;
    z-index: 2;
  }

  .knowledge-card::before {
    background: linear-gradient(90deg, rgba(13, 148, 136, 0.68), rgba(13, 148, 136, 0.08));
    content: "";
    height: 2px;
    left: -300px;
    position: absolute;
    top: 28px;
    width: 300px;
  }

  .knowledge-card::after {
    background: var(--teal);
    border: 3px solid #fff;
    border-radius: 50%;
    box-shadow: 0 0 0 3px rgba(13, 148, 136, 0.12);
    content: "";
    height: 10px;
    left: -306px;
    position: absolute;
    top: 24px;
    width: 10px;
  }
}

@media (max-width: 1699px) {
  .knowledge-card {
    margin-top: 16px;
  }

  .knowledge-card::before {
    background: rgba(13, 148, 136, 0.45);
    content: "";
    display: block;
    height: 22px;
    margin: -16px 0 10px 18px;
    width: 2px;
  }
}

.challenge-overlay {
  align-items: center;
  background: rgba(12, 18, 32, 0.5);
  display: flex;
  inset: 0;
  justify-content: center;
  padding: 20px;
  position: fixed;
  z-index: 90;
}

.challenge-overlay[hidden] {
  display: none;
}

.challenge-open {
  overflow: hidden;
}

.challenge-panel {
  background: #fff;
  border: 1px solid var(--line);
  border-radius: 8px;
  box-shadow: 0 30px 80px rgba(12, 18, 32, 0.28);
  max-height: min(760px, 92vh);
  max-width: 760px;
  overflow-y: auto;
  padding: clamp(20px, 4vw, 30px);
  position: relative;
  width: min(100%, 760px);
}

.challenge-close {
  background: #fff;
  border: 1px solid var(--line);
  border-radius: 50%;
  color: var(--muted);
  cursor: pointer;
  font-size: 1.4rem;
  height: 34px;
  position: absolute;
  right: 18px;
  top: 18px;
  width: 34px;
}

.challenge-head {
  align-items: flex-start;
  border-bottom: 1px solid var(--line);
  display: flex;
  gap: 18px;
  justify-content: space-between;
  margin-bottom: 20px;
  padding: 0 44px 16px 0;
}

.challenge-kicker,
.challenge-progress,
.challenge-score {
  color: var(--teal);
  font-size: 0.86rem;
  font-weight: 700;
}

.challenge-meta {
  display: grid;
  gap: 4px;
  justify-items: end;
  text-align: right;
  white-space: nowrap;
}

.challenge-score {
  color: var(--muted);
}

.challenge-head h2 {
  font-size: clamp(1.7rem, 5vw, 2.6rem);
  line-height: 1.1;
  margin: 4px 0 0;
}

.challenge-question-title {
  font-size: 1.12rem;
  font-weight: 700;
  line-height: 1.65;
  margin: 0;
}

.challenge-question {
  color: var(--text);
  display: grid;
  gap: 10px;
  line-height: 1.7;
  margin: 10px 0 0;
}

.challenge-question p {
  margin: 0;
}

.challenge-question ol,
.challenge-question ul {
  margin: 0;
  padding-left: 1.35rem;
}

.challenge-question .math-box {
  margin: 8px 0;
  overflow-x: auto;
}

.challenge-question figure {
  margin: 8px 0;
}

.challenge-question img {
  max-height: 260px;
  object-fit: contain;
}

.challenge-hint {
  color: var(--muted);
  font-size: 0.92rem;
  margin: 10px 0 14px;
}

.challenge-options,
.challenge-fills {
  display: grid;
  gap: 10px;
}

.challenge-option {
  background: #fff;
  border: 1px solid var(--line);
  border-radius: 8px;
  color: var(--text);
  cursor: pointer;
  font: inherit;
  line-height: 1.5;
  padding: 12px 14px;
  text-align: left;
}

.challenge-option:hover,
.challenge-option.is-selected {
  background: rgba(37, 99, 235, 0.08);
  border-color: rgba(37, 99, 235, 0.32);
}

.challenge-option.is-correct-option {
  background: rgba(13, 148, 136, 0.12);
  border-color: rgba(13, 148, 136, 0.42);
  color: #0f766e;
}

.challenge-option.is-wrong-option {
  background: rgba(225, 77, 90, 0.1);
  border-color: rgba(225, 77, 90, 0.38);
  color: #b42332;
}

.challenge-fill {
  display: grid;
  gap: 6px;
}

.challenge-fill span {
  color: var(--muted);
  font-size: 0.9rem;
  font-weight: 700;
}

.challenge-fill input {
  border: 1px solid var(--line);
  border-radius: 8px;
  font: inherit;
  min-height: 42px;
  padding: 0 12px;
}

.challenge-fill input.is-correct-fill {
  border-color: rgba(13, 148, 136, 0.6);
  box-shadow: 0 0 0 3px rgba(13, 148, 136, 0.12);
}

.challenge-fill input.is-wrong-fill {
  border-color: rgba(225, 77, 90, 0.58);
  box-shadow: 0 0 0 3px rgba(225, 77, 90, 0.1);
}

.challenge-result {
  border-radius: 8px;
  display: grid;
  gap: 4px;
  margin: 16px 0 0;
  min-height: 24px;
  padding: 0;
}

.challenge-result.is-correct,
.challenge-result.is-wrong {
  padding: 12px 14px;
}

.challenge-result.is-correct {
  background: rgba(13, 148, 136, 0.1);
  color: #0f766e;
}

.challenge-result.is-wrong {
  background: rgba(225, 77, 90, 0.1);
  color: #b42332;
}

.challenge-actions {
  display: flex;
  flex-wrap: wrap;
  gap: 10px;
  margin-top: 18px;
}

.challenge-finish {
  align-items: center;
  display: grid;
  gap: 8px;
  min-height: 180px;
  text-align: center;
}

.challenge-finish strong {
  font-size: 2rem;
}

pre {
  overflow-x: auto;
  background: #111827;
  color: #f8fafc;
  border-radius: 10px;
  padding: 16px;
  line-height: 1.55;
}

code {
  font-family: ui-monospace, SFMono-Regular, Consolas, "Liberation Mono", monospace;
  font-size: 0.94em;
}

:not(pre) > code {
  background: rgba(37, 99, 235, 0.08);
  border-radius: 4px;
  color: #1d4ed8;
  padding: 2px 5px;
}

#particle-line-bg {
  height: 100%;
  left: 0;
  opacity: 0.75;
  pointer-events: none;
  position: fixed;
  top: 0;
  width: 100%;
  z-index: 0;
}

.click-word {
  animation: clickWordFloat 1.2s ease-out forwards;
  font-size: 18px;
  font-weight: 700;
  pointer-events: none;
  position: fixed;
  text-shadow: 0 2px 6px rgba(0, 0, 0, 0.18);
  user-select: none;
  white-space: nowrap;
  z-index: 999999;
}

@keyframes clickWordFloat {
  0% {
    opacity: 1;
    transform: translate(-50%, -50%) scale(0.8);
  }

  30% {
    opacity: 1;
    transform: translate(-50%, -80%) scale(1.15);
  }

  100% {
    opacity: 0;
    transform: translate(-50%, -150%) scale(1);
  }
}

@keyframes cursorBlink {
  0%,
  45% {
    opacity: 1;
  }

  46%,
  100% {
    opacity: 0;
  }
}

@media (prefers-reduced-motion: reduce) {
  .click-word,
  .typewriter-cursor::after {
    animation: none;
  }

  #particle-line-bg {
    display: none;
  }
}

.site-footer {
  border-top: 1px solid var(--line);
  background: var(--surface);
}

.footer-inner {
  padding: 22px 0;
  color: var(--muted);
  font-size: 0.9rem;
}

.empty-state {
  padding: 24px;
  border: 1px dashed var(--line);
  border-radius: 8px;
  color: var(--muted);
  background: var(--surface);
}

@media (max-width: 860px) {
  .header-inner,
  .toolbar {
    align-items: flex-start;
    flex-direction: column;
  }

  .main-grid,
  .article-layout,
  .intro {
    grid-template-columns: 1fr;
  }

  .article-layout {
    padding-left: 12px;
    padding-right: 12px;
  }

  .article-toc {
    order: -1;
    position: static;
  }

  .article-toc-inner {
    max-height: none;
  }

  .article-toc nav {
    grid-template-columns: repeat(auto-fit, minmax(120px, 1fr));
    max-height: 320px;
  }

  .article-toc .toc-level-3,
  .article-toc .toc-level-4 {
    padding-left: 10px;
  }

  .intro img {
    max-width: 320px;
  }

  .nav-links {
    flex-wrap: wrap;
    white-space: normal;
  }
}

/* Course-first learning hub */
:root {
  --ink: #14231f;
  --cream: #f5f3ed;
  --cream-deep: #ebe7dc;
  --learning-green: #174d3d;
  --learning-lime: #d9f99d;
  --learning-orange: #f47a55;
}

.home-page .site-header {
  display: block;
}

.home-page .site-shell,
.course-page .site-shell {
  background: var(--cream);
}

.home-page .site-header,
.course-page .site-header {
  background: rgba(245, 243, 237, 0.9);
  border-color: rgba(20, 35, 31, 0.1);
}

.home-page .header-inner,
.course-page .header-inner,
.home-page .footer-inner,
.course-page .footer-inner {
  width: min(1240px, calc(100% - 48px));
}

.home-page .brand img,
.course-page .brand img {
  box-shadow: none;
}

.home-page .nav-links a,
.course-page .nav-links a {
  color: #40534d;
  font-weight: 600;
}

.home-page .menu-button,
.course-page .menu-button {
  background: var(--learning-green);
  border-color: var(--learning-green);
  border-radius: 999px;
}

.home-page .theme-switch,
.course-page .theme-switch {
  border-color: rgba(20, 35, 31, 0.25);
}

.home-hero {
  align-items: center;
  background:
    radial-gradient(circle at 82% 18%, rgba(217, 249, 157, 0.24), transparent 24%),
    var(--learning-green);
  color: #fff;
  display: grid;
  gap: clamp(38px, 7vw, 90px);
  grid-template-columns: minmax(0, 1.15fr) minmax(320px, 0.7fr);
  min-height: 680px;
  overflow: hidden;
  padding: 96px max(24px, calc((100vw - 1240px) / 2));
  text-align: left;
}

.home-hero::after {
  background-image: linear-gradient(rgba(255, 255, 255, 0.035) 1px, transparent 1px), linear-gradient(90deg, rgba(255, 255, 255, 0.035) 1px, transparent 1px);
  background-size: 56px 56px;
}

.theme-dim .home-hero::after,
.drawer-open .home-hero::after {
  background-color: rgba(5, 12, 10, 0.26);
}

.hero-content {
  max-width: 760px;
  min-width: 0;
  text-shadow: none;
}

.hero-kicker {
  align-items: center;
  color: var(--learning-lime);
  display: flex;
  font: 700 0.78rem/1.2 ui-monospace, SFMono-Regular, Consolas, monospace;
  gap: 10px;
  letter-spacing: 0.16em;
  margin: 0 0 26px;
}

.hero-kicker span {
  background: var(--learning-lime);
  border-radius: 50%;
  height: 7px;
  width: 7px;
}

.hero-content h1 {
  font-family: "Microsoft YaHei", ui-sans-serif, system-ui, sans-serif;
  font-size: clamp(3.2rem, 6.6vw, 6.35rem);
  font-weight: 800;
  letter-spacing: -0.075em;
  line-height: 0.98;
}

.hero-content h1 em {
  color: var(--learning-lime);
  font-family: "LXGW WenKai", "STKaiti", serif;
  font-style: normal;
  font-size: 0.82em;
  font-weight: 500;
  letter-spacing: -0.05em;
  white-space: nowrap;
}

.hero-content .hero-description {
  color: rgba(255, 255, 255, 0.72);
  font-family: inherit;
  font-size: 1.06rem;
  line-height: 1.85;
  margin: 30px 0 0;
  max-width: 650px;
}

.hero-actions {
  align-items: center;
  display: flex;
  flex-wrap: wrap;
  gap: 24px;
  margin-top: 34px;
}

.hero-actions a {
  color: #fff;
  font-weight: 700;
}

.primary-action {
  align-items: center;
  background: var(--learning-orange);
  border-radius: 999px;
  display: inline-flex;
  gap: 32px;
  min-height: 54px;
  padding: 0 24px;
}

.primary-action:hover {
  background: #fa8c69;
  text-decoration: none;
  transform: translateY(-2px);
}

.secondary-action {
  border-bottom: 1px solid rgba(255, 255, 255, 0.45);
  padding: 8px 0;
}

.hero-stats {
  display: flex;
  gap: clamp(24px, 5vw, 64px);
  margin-top: 52px;
}

.hero-stats div {
  display: grid;
}

.hero-stats strong {
  color: #fff;
  font: 700 1.75rem/1 ui-monospace, SFMono-Regular, Consolas, monospace;
}

.hero-stats span {
  color: rgba(255, 255, 255, 0.54);
  font-size: 0.8rem;
  margin-top: 7px;
}

.hero-board {
  background: #f8f4e9;
  border-radius: 4px 28px 4px 4px;
  box-shadow: 24px 28px 0 rgba(7, 34, 26, 0.54);
  color: var(--ink);
  padding: 20px;
  position: relative;
  transform: rotate(1.2deg);
  width: 100%;
  z-index: 2;
}

.hero-board::before {
  background: var(--learning-orange);
  content: "";
  height: 12px;
  position: absolute;
  right: 28px;
  top: -6px;
  transform: rotate(-7deg);
  width: 88px;
}

.hero-board-head {
  align-items: center;
  border-bottom: 1px solid #dcd6c8;
  display: flex;
  font-weight: 800;
  justify-content: space-between;
  padding: 6px 4px 16px;
}

.live-dot {
  color: #63716c;
  font-size: 0.72rem;
  font-weight: 600;
}

.live-dot::before {
  background: #5ea274;
  border-radius: 50%;
  content: "";
  display: inline-block;
  height: 7px;
  margin-right: 6px;
  width: 7px;
}

.hero-board > a {
  align-items: center;
  border-bottom: 1px solid #e1dbcf;
  color: var(--ink);
  display: grid;
  gap: 14px;
  grid-template-columns: 38px 1fr auto;
  padding: 17px 4px;
}

.hero-board > a:hover {
  color: var(--learning-green);
  text-decoration: none;
}

.board-number {
  color: var(--learning-orange);
  font: 700 0.82rem/1 ui-monospace, SFMono-Regular, Consolas, monospace;
}

.hero-board a strong,
.hero-board a small {
  display: block;
}

.hero-board a small {
  color: #78827e;
  font-size: 0.73rem;
  margin-top: 3px;
}

.hero-board a em {
  font-style: normal;
}

.hero-board-note {
  color: #7a837f;
  font-size: 0.78rem;
  line-height: 1.6;
  padding: 16px 4px 3px;
}

.hero-orbit {
  border: 1px solid rgba(217, 249, 157, 0.12);
  border-radius: 50%;
  pointer-events: none;
  position: absolute;
}

.hero-orbit-one {
  height: 420px;
  right: -160px;
  top: -210px;
  width: 420px;
}

.hero-orbit-two {
  bottom: -360px;
  height: 680px;
  left: -340px;
  width: 680px;
}

.learning-section,
.latest-section,
.learning-callout,
.course-page-main,
.article-breadcrumb {
  margin-left: auto;
  margin-right: auto;
  width: min(1240px, calc(100% - 48px));
}

.learning-section {
  padding: 94px 0 70px;
}

.latest-section {
  padding: 28px 0 94px;
}

.section-heading {
  align-items: end;
  display: grid;
  gap: 40px;
  grid-template-columns: minmax(0, 1fr) minmax(280px, 0.7fr);
  margin-bottom: 36px;
}

.section-heading > div > p,
.curriculum-heading p,
.course-sidebar section > p {
  color: #c45d3e;
  font: 700 0.76rem/1.2 ui-monospace, SFMono-Regular, Consolas, monospace;
  letter-spacing: 0.17em;
  margin: 0 0 12px;
}

.section-heading h2,
.curriculum-heading h2,
.course-sidebar h2 {
  color: var(--ink);
  font-size: clamp(2rem, 4vw, 3.2rem);
  letter-spacing: -0.05em;
  line-height: 1.12;
  margin: 0;
}

.section-heading > p {
  color: #65736e;
  line-height: 1.8;
  margin: 0;
}

.course-search {
  align-items: center;
  background: #fff;
  border: 1px solid #ded9cc;
  border-radius: 999px;
  display: flex;
  gap: 12px;
  margin-bottom: 26px;
  max-width: 620px;
  min-height: 50px;
  padding: 0 17px;
}

.course-search input {
  background: transparent;
  border: 0;
  color: var(--ink);
  flex: 1;
  font: inherit;
  outline: 0;
}

.course-search kbd {
  background: #f0eee7;
  border: 1px solid #ded9cc;
  border-radius: 5px;
  color: #7c8581;
  font-size: 0.7rem;
  padding: 2px 7px;
}

.course-grid {
  display: grid;
  gap: 18px;
  grid-template-columns: repeat(2, minmax(0, 1fr));
}

.course-card {
  --course-color: #287d65;
  background: #fff;
  border: 1px solid #ded9cc;
  border-radius: 4px 22px 4px 4px;
  display: flex;
  flex-direction: column;
  min-height: 440px;
  overflow: hidden;
  padding: 28px;
  position: relative;
}

.course-card::before {
  background: var(--course-color);
  content: "";
  height: 4px;
  left: 0;
  position: absolute;
  right: 0;
  top: 0;
}

.course-coral { --course-color: #e66f4d; }
.course-violet { --course-color: #7161a8; }
.course-teal { --course-color: #247d68; }
.course-blue { --course-color: #4678a8; }

.course-card-top {
  align-items: center;
  display: flex;
  justify-content: space-between;
}

.course-icon {
  align-items: center;
  background: color-mix(in srgb, var(--course-color) 12%, white);
  border-radius: 12px;
  color: var(--course-color);
  display: inline-flex;
  font-size: 1.45rem;
  height: 48px;
  justify-content: center;
  width: 48px;
}

.course-index {
  color: #c4c1b8;
  font: 700 0.82rem/1 ui-monospace, SFMono-Regular, Consolas, monospace;
}

.course-eyebrow {
  color: var(--course-color);
  font: 700 0.72rem/1.2 ui-monospace, SFMono-Regular, Consolas, monospace;
  letter-spacing: 0.13em;
  margin: 24px 0 10px;
  text-transform: uppercase;
}

.course-card h3 {
  color: var(--ink);
  font-size: 1.75rem;
  letter-spacing: -0.04em;
  line-height: 1.2;
  margin: 0;
}

.course-card > p:not(.course-eyebrow) {
  color: #6a7772;
  font-size: 0.92rem;
  margin: 12px 0 20px;
}

.course-preview {
  border-top: 1px solid #ebe7dc;
  list-style: none;
  margin: auto 0 0;
  padding: 12px 0 0;
}

.course-preview li {
  align-items: baseline;
  color: #42524d;
  display: grid;
  font-size: 0.82rem;
  gap: 10px;
  grid-template-columns: 24px 1fr;
  padding: 5px 0;
}

.course-preview span {
  color: #a7aaa4;
  font: 600 0.68rem/1 ui-monospace, SFMono-Regular, Consolas, monospace;
}

.course-preview strong {
  font-weight: 600;
  overflow: hidden;
  text-overflow: ellipsis;
  white-space: nowrap;
}

.course-enter {
  align-items: center;
  border-top: 1px solid #ebe7dc;
  color: var(--ink);
  display: flex;
  font-weight: 800;
  justify-content: space-between;
  margin: 16px -28px -28px;
  padding: 15px 28px;
}

.course-enter:hover {
  background: var(--course-color);
  color: #fff;
  text-decoration: none;
}

.section-heading.compact {
  align-items: end;
  grid-template-columns: 1fr auto;
}

.section-heading.compact a {
  color: var(--learning-green);
  font-weight: 700;
}

.lesson-rows {
  border-top: 1px solid #d8d3c6;
}

.lesson-row {
  align-items: center;
  border-bottom: 1px solid #d8d3c6;
  color: var(--ink);
  display: grid;
  gap: 22px;
  grid-template-columns: 100px 1fr auto 28px;
  padding: 22px 8px;
}

.lesson-row:hover {
  background: rgba(255, 255, 255, 0.52);
  padding-left: 18px;
  padding-right: 18px;
  text-decoration: none;
}

.lesson-type,
.course-lesson-type {
  color: #c45d3e;
  font: 700 0.72rem/1.2 ui-monospace, SFMono-Regular, Consolas, monospace;
}

.lesson-row-main strong,
.lesson-row-main small {
  display: block;
}

.lesson-row-main strong {
  font-size: 1.03rem;
}

.lesson-row-main small,
.lesson-row time {
  color: #7a8581;
  font-size: 0.78rem;
  margin-top: 3px;
}

.lesson-arrow {
  font-size: 1.15rem;
}

.learning-callout {
  align-items: center;
  background: #dfedc2;
  border-radius: 4px 24px 4px 4px;
  display: grid;
  gap: 42px;
  grid-template-columns: minmax(300px, 1.1fr) 0.75fr auto;
  margin-bottom: 96px;
  padding: 44px;
}

.learning-callout h2,
.learning-callout p {
  margin: 0;
}

.learning-callout > div > p {
  color: #5d7650;
  font-size: 0.8rem;
  font-weight: 700;
}

.learning-callout h2 {
  color: var(--ink);
  font-size: clamp(1.7rem, 3.1vw, 2.65rem);
  letter-spacing: -0.05em;
  line-height: 1.18;
  margin-top: 5px;
}

.learning-callout > p {
  color: #596d60;
  font-size: 0.9rem;
}

.learning-callout > a {
  background: var(--learning-green);
  border-radius: 999px;
  color: #fff;
  font-weight: 700;
  padding: 13px 20px;
  white-space: nowrap;
}

.learning-callout > a:hover {
  text-decoration: none;
}

.home-page .site-footer,
.course-page .site-footer {
  background: var(--ink);
  border: 0;
  color: #fff;
}

.home-page .footer-inner,
.course-page .footer-inner {
  align-items: center;
  color: rgba(255, 255, 255, 0.55);
  display: flex;
  gap: 20px;
  justify-content: space-between;
  min-height: 82px;
}

.footer-inner strong {
  color: inherit;
}

/* Course overview */
.course-page-main {
  padding: 38px 0 90px;
}

.breadcrumb {
  align-items: center;
  color: #80908a;
  display: flex;
  flex-wrap: wrap;
  font-size: 0.8rem;
  gap: 8px;
  margin-bottom: 22px;
}

.breadcrumb a {
  color: #60736c;
}

.breadcrumb strong {
  color: var(--ink);
}

.course-hero {
  --course-color: #247d68;
  align-items: center;
  background: var(--learning-green);
  border-radius: 4px 32px 4px 4px;
  color: #fff;
  display: grid;
  gap: 40px;
  grid-template-columns: 1fr auto;
  min-height: 360px;
  overflow: hidden;
  padding: clamp(38px, 6vw, 72px);
  position: relative;
}

.course-hero::after {
  border: 1px solid rgba(255, 255, 255, 0.11);
  border-radius: 50%;
  content: "";
  height: 460px;
  position: absolute;
  right: -160px;
  top: -190px;
  width: 460px;
}

.course-hero > div {
  max-width: 740px;
  position: relative;
  z-index: 1;
}

.course-hero .course-eyebrow {
  color: var(--learning-lime);
  margin-top: 0;
}

.course-hero h1 {
  font-size: clamp(2.8rem, 6vw, 5.4rem);
  letter-spacing: -0.065em;
  line-height: 1;
  margin: 0;
}

.course-hero > div > p:not(.course-eyebrow) {
  color: rgba(255, 255, 255, 0.7);
  font-size: 1rem;
  line-height: 1.85;
  margin: 24px 0;
  max-width: 660px;
}

.course-hero-meta {
  display: flex;
  flex-wrap: wrap;
  gap: 10px 24px;
}

.course-hero-meta span {
  color: rgba(255, 255, 255, 0.62);
  font-size: 0.8rem;
}

.course-hero-icon {
  align-items: center;
  border: 1px solid rgba(255, 255, 255, 0.18);
  border-radius: 32px;
  color: var(--learning-lime);
  display: flex;
  font-size: 5rem;
  height: 180px;
  justify-content: center;
  position: relative;
  transform: rotate(5deg);
  width: 180px;
  z-index: 1;
}

.course-layout {
  align-items: start;
  display: grid;
  gap: 36px;
  grid-template-columns: minmax(0, 1fr) 300px;
  margin-top: 54px;
}

.curriculum-heading {
  align-items: end;
  display: flex;
  gap: 22px;
  justify-content: space-between;
  margin-bottom: 22px;
}

.curriculum-heading h2 {
  font-size: 2.3rem;
}

.curriculum-heading > span {
  color: #71807a;
  font-size: 0.8rem;
}

.course-lessons {
  display: grid;
  gap: 12px;
}

.course-chapter + .course-chapter {
  margin-top: 28px;
}

.course-chapter-heading {
  display: flex;
  align-items: center;
  gap: 12px;
  margin: 0 0 12px;
  padding: 0 4px;
}

.course-chapter-heading > span {
  color: var(--accent, #3b82f6);
  font-size: 0.75rem;
  font-weight: 800;
  letter-spacing: 0.08em;
}

.course-chapter-heading h3 {
  margin: 0;
  color: var(--ink, #152033);
  font-size: 1.15rem;
}

.course-chapter-heading small {
  margin-left: auto;
  color: var(--muted, #738096);
}

.course-chapter-lessons {
  display: grid;
  gap: 12px;
}

.article-callout {
  margin: 1.5rem 0;
  padding: 1rem 1.15rem;
  border: 1px solid #bfdbfe;
  border-left: 4px solid #3b82f6;
  border-radius: 12px;
  background: #eff6ff;
}

.article-callout > strong {
  display: block;
  margin-bottom: 0.45rem;
  color: #1d4ed8;
}

.article-callout.warningbox {
  border-color: #fecaca;
  border-left-color: #ef4444;
  background: #fff1f2;
}

.article-callout.warningbox > strong {
  color: #b91c1c;
}

.article-callout.examplebox {
  border-color: #bbf7d0;
  border-left-color: #22c55e;
  background: #f0fdf4;
}

.article-callout.examplebox > strong {
  color: #15803d;
}

.course-lesson {
  align-items: center;
  background: #fff;
  border: 1px solid #ded9cc;
  border-radius: 4px 16px 4px 4px;
  color: var(--ink);
  display: grid;
  gap: 22px;
  grid-template-columns: 52px 1fr 130px;
  padding: 22px;
}

.course-lesson:hover {
  border-color: #8aa597;
  box-shadow: 0 14px 32px rgba(36, 65, 55, 0.08);
  text-decoration: none;
  transform: translateY(-2px);
}

.course-lesson-index {
  align-items: center;
  background: #edf3e3;
  border-radius: 50%;
  color: var(--learning-green);
  display: flex;
  font: 700 0.8rem/1 ui-monospace, SFMono-Regular, Consolas, monospace;
  height: 46px;
  justify-content: center;
  width: 46px;
}

.course-lesson-content,
.course-lesson-content > strong,
.course-lesson-content > small {
  display: block;
}

.course-lesson-content > strong {
  font-size: 1.08rem;
  line-height: 1.35;
  margin: 5px 0;
}

.course-lesson-content > small {
  color: #76827d;
  line-height: 1.55;
}

.course-lesson-tags {
  display: flex;
  flex-wrap: wrap;
  gap: 5px;
  margin-top: 9px;
}

.course-lesson-tags span {
  background: #f2f0e9;
  border-radius: 999px;
  color: #77817d;
  font-size: 0.66rem;
  padding: 2px 7px;
}

.course-lesson-meta {
  color: #7b8682;
  display: grid;
  font-size: 0.7rem;
  gap: 3px;
  justify-items: end;
}

.course-lesson-meta em {
  color: var(--learning-green);
  font-size: 0.78rem;
  font-style: normal;
  font-weight: 700;
  margin-top: 8px;
}

.course-sidebar {
  display: grid;
  gap: 14px;
  position: sticky;
  top: 94px;
}

.course-sidebar section {
  background: #fff;
  border: 1px solid #ded9cc;
  padding: 24px;
}

.course-sidebar h2 {
  font-size: 1.2rem;
}

.course-sidebar ul {
  display: grid;
  gap: 12px;
  list-style: none;
  margin: 20px 0 0;
  padding: 0;
}

.course-sidebar li {
  align-items: center;
  color: #607069;
  display: flex;
  font-size: 0.86rem;
  gap: 10px;
}

.course-sidebar li span {
  align-items: center;
  background: #e5f1d4;
  border-radius: 50%;
  color: var(--learning-green);
  display: flex;
  height: 22px;
  justify-content: center;
  width: 22px;
}

.course-sidebar .course-tip {
  background: #dfedc2;
  border: 0;
}

.course-tip > span {
  color: var(--learning-green);
  font-size: 0.78rem;
  font-weight: 800;
}

.course-tip p {
  color: #60705d;
  font-size: 0.82rem;
  line-height: 1.7;
  margin-bottom: 0;
}

.back-all-courses {
  color: var(--learning-green);
  font-size: 0.84rem;
  font-weight: 700;
  padding: 8px;
}

/* Article course context */
.article-breadcrumb {
  margin-bottom: 0;
  margin-top: 26px;
}

.article-page .article-layout {
  padding-top: 16px;
}

.article-page .article-header::before {
  color: var(--teal);
  content: "COURSE LESSON";
  display: block;
  font: 700 0.72rem/1.2 ui-monospace, SFMono-Regular, Consolas, monospace;
  letter-spacing: 0.16em;
  margin-bottom: 12px;
}

@media (max-width: 980px) {
  .home-hero {
    grid-template-columns: 1fr;
    padding-bottom: 86px;
  }

  .hero-board {
    max-width: 600px;
  }

  .course-layout {
    grid-template-columns: 1fr;
  }

  .course-sidebar {
    grid-template-columns: 1fr 1fr;
    position: static;
  }

  .learning-callout {
    grid-template-columns: 1fr 1fr;
  }

  .learning-callout > a {
    justify-self: start;
  }
}

@media (max-width: 700px) {
  .home-page .header-inner,
  .course-page .header-inner,
  .home-page .footer-inner,
  .course-page .footer-inner,
  .learning-section,
  .latest-section,
  .learning-callout,
  .course-page-main,
  .article-breadcrumb {
    width: min(100% - 28px, 1240px);
  }

  .home-page .header-inner,
  .course-page .header-inner {
    align-items: center;
    flex-direction: row;
  }

  .home-page .nav-links,
  .course-page .nav-links {
    display: none;
  }

  .home-page .menu-button,
  .course-page .menu-button {
    height: 36px;
    left: 14px;
    overflow: hidden;
    padding: 0;
    top: 82px;
    width: 36px;
  }

  .home-page .menu-button span:last-child,
  .course-page .menu-button span:last-child {
    display: none;
  }

  .home-page .theme-switch,
  .course-page .theme-switch {
    right: 14px;
    top: 82px;
  }

  .home-hero {
    min-height: auto;
    padding: 88px 20px 70px;
  }

  .hero-content h1 {
    font-size: clamp(2.8rem, 14vw, 4.4rem);
  }

  .hero-content h1 em {
    display: block;
    font-size: 0.7em;
    line-height: 1.16;
    white-space: nowrap;
  }

  .hero-board,
  .hero-board > a,
  .hero-board > a > span {
    min-width: 0;
  }

  .hero-board a strong,
  .hero-board a small {
    overflow: hidden;
    text-overflow: ellipsis;
    white-space: nowrap;
  }

  .hero-stats {
    gap: 25px;
  }

  .hero-board {
    box-shadow: 12px 14px 0 rgba(7, 34, 26, 0.54);
    transform: none;
  }

  .learning-section {
    padding-top: 68px;
  }

  .section-heading,
  .course-grid,
  .learning-callout {
    grid-template-columns: 1fr;
  }

  .section-heading {
    gap: 16px;
  }

  .course-card {
    min-height: 410px;
  }

  .lesson-row {
    gap: 7px 12px;
    grid-template-columns: 82px 1fr 24px;
  }

  .lesson-row time {
    display: none;
  }

  .learning-callout {
    gap: 20px;
    padding: 28px;
  }

  .home-page .footer-inner,
  .course-page .footer-inner {
    align-items: flex-start;
    flex-direction: column;
    gap: 4px;
    padding: 22px 0;
  }

  .course-hero {
    grid-template-columns: 1fr;
    padding: 34px 26px;
  }

  .course-hero-icon {
    display: none;
  }

  .course-layout {
    margin-top: 38px;
  }

  .course-lesson {
    align-items: start;
    grid-template-columns: 40px 1fr;
    padding: 18px 14px;
  }

  .course-lesson-index {
    height: 38px;
    width: 38px;
  }

  .course-lesson-meta {
    display: none;
  }

  .course-sidebar {
    grid-template-columns: 1fr;
  }
}

/* Quiet, image-led home masthead */
.home-page .site-header {
  background: linear-gradient(180deg, rgba(7, 20, 43, 0.58), rgba(7, 20, 43, 0));
  border: 0;
  box-shadow: none;
  left: 0;
  position: absolute;
  right: 0;
  top: 0;
}

.home-page .site-header .brand,
.home-page .site-header .brand strong {
  color: rgba(255, 255, 255, 0.96);
}

.home-page .site-header .brand > span > span {
  color: rgba(255, 255, 255, 0.62);
}

.home-page .site-header .brand img {
  background: rgba(255, 255, 255, 0.88);
  border-radius: 7px;
  padding: 3px;
}

.home-page .site-header .nav-links a {
  color: rgba(255, 255, 255, 0.78);
  font-weight: 500;
  text-shadow: 0 2px 12px rgba(4, 13, 31, 0.34);
}

.home-page .site-header .nav-links a:hover {
  color: #fff;
  text-decoration: none;
}

.home-page .home-hero {
  min-height: 100vh;
  padding-top: 122px;
}

.hero-entry {
  align-items: center;
  display: flex;
  flex-direction: column;
  margin-top: 29px;
}

.hero-entry a {
  align-items: center;
  border-bottom: 1px solid rgba(255, 255, 255, 0.52);
  color: rgba(255, 255, 255, 0.94);
  display: inline-flex;
  font-size: 0.94rem;
  font-weight: 600;
  gap: 15px;
  letter-spacing: 0.06em;
  padding: 5px 1px 7px;
  transition: border-color 0.2s ease, color 0.2s ease, transform 0.2s ease;
}

.hero-entry a:hover {
  border-color: #fff;
  color: #fff;
  text-decoration: none;
  transform: translateY(-1px);
}

.hero-entry p {
  color: rgba(255, 255, 255, 0.54);
  font-family: ui-monospace, SFMono-Regular, Consolas, monospace;
  font-size: 0.72rem;
  letter-spacing: 0.04em;
  margin: 24px 0 0;
}

@media (max-width: 700px) {
  .home-page .site-header {
    background: linear-gradient(180deg, rgba(7, 20, 43, 0.74), rgba(7, 20, 43, 0));
  }

  .home-page .site-header .brand {
    margin-left: 54px;
  }

  .home-page .site-header .brand > span,
  .home-page .site-header .nav-links {
    display: none;
  }

  .home-page .home-hero {
    padding-top: 112px;
  }

  .hero-entry p {
    font-size: 0.66rem;
    line-height: 1.75;
    max-width: 280px;
  }
}

/* Answers and explanations stay directly inside each question. */
.knowledge-card,
.qa-card [data-knowledge-card] {
  display: none !important;
}

.qa-answer-stack {
  border-top: 1px dashed rgba(105, 129, 154, 0.24);
  display: grid;
  gap: 10px;
  margin-top: 16px;
  padding-top: 16px;
}

.qa-answer-stack[hidden] {
  display: none;
}

.qa-answer-stack .answer-line,
.qa-answer-stack .explanation-line {
  margin: 0;
  padding: 13px 15px;
}

.qa-answer-stack .answer-line {
  background: rgba(13, 148, 136, 0.08);
  border-left: 3px solid rgba(13, 148, 136, 0.56);
}

.qa-answer-stack .explanation-line {
  background: rgba(64, 158, 255, 0.07);
  border-left: 3px solid rgba(64, 158, 255, 0.48);
  color: #53677e;
}

.qa-answer-stack .explanation-line > strong {
  color: #356d9d;
}

.qa-answer-stack .math-box {
  max-width: 100%;
  overflow-x: auto;
}

/* Soft visual direction: keeps the original airy, romantic blog character. */
:root {
  --soft-sky: #eaf4fb;
  --soft-mint: #e9f5f1;
  --soft-rose: #fff0f2;
  --soft-lilac: #f2effb;
  --soft-ink: #273549;
  --soft-muted: #728096;
  --soft-line: rgba(105, 129, 154, 0.18);
  --soft-shadow: 0 18px 48px rgba(75, 102, 132, 0.1);
}

.home-page .site-shell,
.course-page .site-shell {
  background:
    radial-gradient(circle at 10% 24%, rgba(185, 224, 239, 0.2), transparent 24%),
    radial-gradient(circle at 90% 72%, rgba(244, 207, 216, 0.18), transparent 28%),
    #f8fafc;
}

.home-page .site-header,
.course-page .site-header {
  background: rgba(255, 255, 255, 0.83);
  border-color: rgba(116, 139, 164, 0.16);
  box-shadow: 0 8px 28px rgba(72, 99, 130, 0.05);
}

.home-page .nav-links a,
.course-page .nav-links a,
.breadcrumb a {
  color: #60738d;
}

.home-page .menu-button,
.course-page .menu-button {
  background: rgba(46, 69, 94, 0.28);
  border: 1px solid rgba(255, 255, 255, 0.62);
  border-radius: 6px;
  backdrop-filter: blur(9px);
}

.home-hero {
  background:
    linear-gradient(180deg, rgba(16, 29, 52, 0.12), rgba(26, 34, 61, 0.3)),
    url("hero-bg.png") center 70% / cover no-repeat;
  display: flex;
  justify-content: center;
  min-height: calc(100vh - 72px);
  padding: 96px 24px 76px;
  text-align: center;
}

.home-hero::after {
  background: linear-gradient(180deg, rgba(8, 20, 42, 0.04), rgba(9, 21, 43, 0.2));
  background-size: auto;
}

.theme-dim .home-hero::after,
.drawer-open .home-hero::after {
  background: rgba(5, 12, 30, 0.4);
}

.hero-content {
  align-items: center;
  display: flex;
  flex-direction: column;
  max-width: 820px;
  text-shadow: 0 6px 22px rgba(11, 24, 48, 0.34);
  width: 100%;
}

.hero-kicker {
  color: rgba(255, 255, 255, 0.76);
  justify-content: center;
  letter-spacing: 0.15em;
  margin-bottom: 18px;
}

.hero-kicker span {
  background: #ffd8de;
  box-shadow: 0 0 0 5px rgba(255, 216, 222, 0.16);
}

.hero-content h1 {
  font-family: "Brush Script MT", "Segoe Script", "LXGW WenKai", cursive;
  font-size: clamp(4.2rem, 10vw, 7.7rem);
  font-weight: 500;
  letter-spacing: 0;
  line-height: 0.96;
}

.hero-motto {
  color: rgba(255, 255, 255, 0.95);
  font-family: "Segoe Script", "LXGW WenKai", cursive;
  font-size: clamp(1.12rem, 2.1vw, 1.5rem);
  letter-spacing: 0.08em;
  margin: 24px 0 0;
}

.hero-content .hero-description {
  color: rgba(255, 255, 255, 0.76);
  font-size: 0.96rem;
  line-height: 1.8;
  margin-top: 17px;
  max-width: 620px;
}

.hero-actions {
  justify-content: center;
  margin-top: 28px;
}

.primary-action {
  background: rgba(255, 255, 255, 0.92);
  box-shadow: 0 12px 32px rgba(16, 33, 59, 0.18);
  color: #344c68 !important;
}

.primary-action:hover {
  background: #fff;
}

.secondary-action {
  color: rgba(255, 255, 255, 0.9) !important;
}

.hero-stats {
  background: rgba(255, 255, 255, 0.12);
  border: 1px solid rgba(255, 255, 255, 0.18);
  border-radius: 18px;
  backdrop-filter: blur(12px);
  gap: 0;
  margin-top: 38px;
  overflow: hidden;
}

.hero-stats div {
  min-width: 118px;
  padding: 14px 24px;
}

.hero-stats div + div {
  border-left: 1px solid rgba(255, 255, 255, 0.16);
}

.hero-stats strong {
  font-family: inherit;
  font-size: 1.45rem;
}

.hero-stats span {
  color: rgba(255, 255, 255, 0.68);
}

.hero-board,
.hero-orbit {
  display: none;
}

.learning-section {
  padding-top: 86px;
}

.section-heading > div > p,
.curriculum-heading p,
.course-sidebar section > p {
  color: #d47787;
  letter-spacing: 0.14em;
}

.section-heading h2,
.curriculum-heading h2,
.course-sidebar h2 {
  color: var(--soft-ink);
  font-weight: 700;
}

.section-heading > p {
  color: var(--soft-muted);
}

.course-search {
  border: 1px solid var(--soft-line);
  box-shadow: 0 10px 28px rgba(79, 107, 137, 0.06);
}

.course-grid {
  gap: 22px;
}

.course-card {
  --course-color: #65a9a1;
  background: linear-gradient(145deg, rgba(234, 244, 251, 0.88), #fff 46%);
  border: 1px solid var(--soft-line);
  border-radius: 22px;
  box-shadow: var(--soft-shadow);
  min-height: 430px;
  padding: 30px;
  transition: transform 0.25s ease, box-shadow 0.25s ease;
}

.course-card:hover {
  box-shadow: 0 24px 58px rgba(75, 102, 132, 0.15);
  transform: translateY(-5px);
}

.course-card::before {
  background: linear-gradient(90deg, transparent, var(--course-color), transparent);
  height: 2px;
  left: 28px;
  opacity: 0.62;
  right: 28px;
}

.course-coral {
  --course-color: #da8794;
  background: linear-gradient(145deg, var(--soft-rose), #fff 46%);
}

.course-violet {
  --course-color: #9286bc;
  background: linear-gradient(145deg, var(--soft-lilac), #fff 46%);
}

.course-teal {
  --course-color: #65a99b;
  background: linear-gradient(145deg, var(--soft-mint), #fff 46%);
}

.course-blue {
  --course-color: #75a5cb;
  background: linear-gradient(145deg, var(--soft-sky), #fff 46%);
}

.course-icon {
  background: rgba(255, 255, 255, 0.75);
  border: 1px solid color-mix(in srgb, var(--course-color) 25%, white);
  border-radius: 50%;
  box-shadow: 0 8px 20px color-mix(in srgb, var(--course-color) 13%, transparent);
}

.course-card h3,
.lesson-row,
.course-lesson {
  color: var(--soft-ink);
}

.course-card > p:not(.course-eyebrow),
.lesson-row-main small,
.lesson-row time {
  color: var(--soft-muted);
}

.course-preview,
.course-enter {
  border-color: var(--soft-line);
}

.course-enter {
  border-radius: 0 0 20px 20px;
  color: #526c86;
  margin-left: -30px;
  margin-right: -30px;
}

.course-enter:hover {
  background: rgba(255, 255, 255, 0.66);
  color: var(--course-color);
}

.lesson-rows {
  background: rgba(255, 255, 255, 0.72);
  border: 1px solid var(--soft-line);
  border-radius: 18px;
  box-shadow: var(--soft-shadow);
  overflow: hidden;
}

.lesson-row {
  border-color: var(--soft-line);
  padding-left: 22px;
  padding-right: 22px;
}

.lesson-row:last-child {
  border-bottom: 0;
}

.lesson-row:hover {
  background: linear-gradient(90deg, rgba(234, 244, 251, 0.66), rgba(255, 240, 242, 0.38));
}

.lesson-type,
.course-lesson-type {
  color: #cb7887;
}

.learning-callout {
  background:
    radial-gradient(circle at 90% 10%, rgba(255, 255, 255, 0.72), transparent 24%),
    linear-gradient(125deg, #e8f4f1, #edf3fb 58%, #faebef);
  border: 1px solid var(--soft-line);
  border-radius: 24px;
  box-shadow: var(--soft-shadow);
}

.learning-callout h2 {
  color: var(--soft-ink);
}

.learning-callout > div > p,
.learning-callout > p {
  color: #708197;
}

.learning-callout > a {
  background: #6e93aa;
  box-shadow: 0 10px 24px rgba(79, 113, 137, 0.18);
}

.home-page .site-footer,
.course-page .site-footer {
  background: rgba(255, 255, 255, 0.82);
  border-top: 1px solid var(--soft-line);
}

.home-page .footer-inner,
.course-page .footer-inner {
  color: var(--soft-muted);
}

/* Softer course overview pages */
.course-hero {
  background:
    linear-gradient(105deg, rgba(30, 51, 78, 0.76), rgba(65, 86, 115, 0.42)),
    url("hero-bg.png") center 64% / cover no-repeat;
  border-radius: 24px;
  box-shadow: 0 22px 58px rgba(53, 78, 107, 0.16);
}

.course-hero::after {
  border-color: rgba(255, 255, 255, 0.16);
}

.course-hero .course-eyebrow {
  color: #f7d9df;
}

.course-hero-icon {
  background: rgba(255, 255, 255, 0.1);
  border-color: rgba(255, 255, 255, 0.26);
  color: #fff0f3;
  backdrop-filter: blur(10px);
}

.course-lesson {
  border: 1px solid var(--soft-line);
  border-radius: 17px;
  box-shadow: 0 12px 32px rgba(75, 102, 132, 0.06);
}

.course-lesson:hover {
  border-color: rgba(109, 158, 177, 0.4);
  box-shadow: 0 18px 42px rgba(75, 102, 132, 0.12);
}

.course-lesson-index {
  background: linear-gradient(145deg, var(--soft-sky), var(--soft-mint));
  color: #55778b;
}

.course-sidebar section {
  border: 1px solid var(--soft-line);
  border-radius: 17px;
  box-shadow: 0 12px 32px rgba(75, 102, 132, 0.06);
}

.course-sidebar .course-tip {
  background: linear-gradient(145deg, var(--soft-mint), var(--soft-sky));
}

.course-tip > span,
.back-all-courses,
.course-lesson-meta em {
  color: #5b8295;
}

.course-tip p {
  color: #6d7e91;
}

@media (max-width: 700px) {
  .home-hero {
    min-height: calc(100vh - 72px);
    padding: 96px 20px 66px;
  }

  .hero-content h1 {
    font-size: clamp(4rem, 20vw, 5.8rem);
  }

  .hero-content {
    overflow: hidden;
  }

  .hero-kicker {
    flex-wrap: wrap;
    font-size: 0.64rem;
    line-height: 1.6;
    max-width: 100%;
    overflow-wrap: anywhere;
    white-space: normal;
  }

  .hero-motto {
    font-size: 1.08rem;
  }

  .hero-stats {
    max-width: 100%;
    width: 100%;
  }

  .hero-stats div {
    min-width: 0;
    padding: 12px 9px;
    width: 33.333%;
  }

  .course-card {
    min-height: 405px;
  }
}

/* Final home masthead override: keep navigation visually inside the hero. */
.home-page .site-header {
  background: linear-gradient(180deg, rgba(7, 20, 43, 0.58), rgba(7, 20, 43, 0));
  border: 0;
  box-shadow: none;
  left: 0;
  position: absolute;
  right: 0;
  top: 0;
}

.home-page .site-header .brand,
.home-page .site-header .brand strong {
  color: rgba(255, 255, 255, 0.96);
}

.home-page .site-header .brand > span > span {
  color: rgba(255, 255, 255, 0.62);
}

.home-page .site-header .nav-links a {
  color: rgba(255, 255, 255, 0.78);
}

.home-page .home-hero {
  min-height: 100vh;
  padding-top: 122px;
}

@media (max-width: 700px) {
  .home-page .site-header {
    background: linear-gradient(180deg, rgba(7, 20, 43, 0.74), rgba(7, 20, 43, 0));
  }

  .home-page .home-hero {
    padding-top: 112px;
  }
}