/* ==========================================================================
   星空体育官网 style.css
   体育知识大模型 / 体育教育AI / 体育规则 / 教练课程 / 体育历史 / 互动学习
   纯静态 CSS3，无第三方框架，无远程字体
   ========================================================================== */

/* ---------- 1. 设计令牌 Design Tokens ---------- */
:root {
  /* 主色：暖白 / 知识深蓝 / 墨灰 / 教育青 / 运动绿 / 提示橙 */
  --color-bg: #faf7f1;
  --color-bg-alt: #f2ede1;
  --color-surface: #ffffff;
  --color-surface-2: #f6f3ec;
  --color-border: #e4ddcc;
  --color-border-strong: #d3c9ae;

  --color-ink: #262a33;
  --color-ink-soft: #565c68;
  --color-ink-faint: #828892;

  --color-deep-blue: #12335e;
  --color-deep-blue-2: #1c4c8c;
  --color-deep-blue-tint: #e8eef6;

  --color-edu-cyan: #0d7a83;
  --color-edu-cyan-tint: #e3f2f1;

  --color-sport-green: #276b45;
  --color-sport-green-tint: #e6f1e8;

  --color-accent-orange: #d97a35;
  --color-accent-orange-tint: #fbeee0;

  --color-fact: #1c4c8c;
  --color-interpretation: #0d7a83;
  --color-example: #276b45;
  --color-opinion: #a15b1f;

  --shadow-sm: 0 1px 2px rgba(18, 51, 94, 0.06);
  --shadow-md: 0 6px 20px rgba(18, 51, 94, 0.09);
  --shadow-lg: 0 16px 40px rgba(18, 51, 94, 0.14);

  --radius-sm: 6px;
  --radius-md: 12px;
  --radius-lg: 20px;

  --font-sans: -apple-system, BlinkMacSystemFont, "Segoe UI", "PingFang SC",
    "Microsoft YaHei", "Hiragino Sans GB", "Noto Sans CJK SC", sans-serif;
  --font-serif-title: "Songti SC", "SimSun", "Noto Serif CJK SC", serif;

  --container-w: 1180px;
  --header-h: 68px;
}

/* ---------- 2. Reset ---------- */
*,
*::before,
*::after {
  box-sizing: border-box;
}

html {
  scroll-behavior: smooth;
  -webkit-text-size-adjust: 100%;
}

body {
  margin: 0;
  background: var(--color-bg);
  color: var(--color-ink);
  font-family: var(--font-sans);
  font-size: 16px;
  line-height: 1.75;
  overflow-x: hidden;
}

img,
svg {
  max-width: 100%;
  height: auto;
  display: block;
}

a {
  color: var(--color-deep-blue-2);
  text-decoration: none;
}

a:hover {
  text-decoration: underline;
}

ul,
ol {
  padding-left: 1.3em;
}

table {
  border-collapse: collapse;
  width: 100%;
}

h1,
h2,
h3,
h4 {
  color: var(--color-deep-blue);
  line-height: 1.4;
  margin: 0 0 0.6em;
  font-weight: 700;
}

h1 { font-size: 1.9rem; }
h2 { font-size: 1.5rem; }
h3 { font-size: 1.2rem; }
h4 { font-size: 1.05rem; }

p { margin: 0 0 1em; }

button {
  font-family: inherit;
}

/* ---------- 3. 布局 Layout ---------- */
.container {
  width: 100%;
  max-width: var(--container-w);
  margin: 0 auto;
  padding: 0 20px;
}

.section {
  padding: 56px 0;
}

.section--alt {
  background: var(--color-bg-alt);
}

.section--surface {
  background: var(--color-surface);
  border-top: 1px solid var(--color-border);
  border-bottom: 1px solid var(--color-border);
}

.section-head {
  max-width: 760px;
  margin: 0 0 32px;
}

.section-head .eyebrow {
  display: inline-block;
  font-size: 0.8rem;
  letter-spacing: 0.06em;
  color: var(--color-edu-cyan);
  font-weight: 700;
  margin-bottom: 8px;
}

.section-head p {
  color: var(--color-ink-soft);
}

.grid {
  display: grid;
  gap: 24px;
}

.grid-2 { grid-template-columns: repeat(2, 1fr); }
.grid-3 { grid-template-columns: repeat(3, 1fr); }
.grid-4 { grid-template-columns: repeat(4, 1fr); }

@media (max-width: 860px) {
  .grid-2, .grid-3, .grid-4 { grid-template-columns: 1fr; }
}

.flow-2col {
  display: grid;
  grid-template-columns: 1.1fr 0.9fr;
  gap: 36px;
  align-items: start;
}

@media (max-width: 860px) {
  .flow-2col { grid-template-columns: 1fr; }
}

/* ---------- 4. Header / Nav ---------- */
.site-header {
  position: sticky;
  top: 0;
  z-index: 100;
  height: var(--header-h);
  display: flex;
  align-items: center;
  background: rgba(250, 247, 241, 0.94);
  backdrop-filter: blur(6px);
  border-bottom: 1px solid var(--color-border);
}

.site-header .container {
  display: flex;
  align-items: center;
  justify-content: space-between;
  gap: 16px;
}

.brand {
  display: flex;
  align-items: center;
  gap: 10px;
  font-weight: 700;
  color: var(--color-deep-blue);
  font-size: 1.08rem;
  flex-shrink: 0;
}

.brand img {
  width: 34px;
  height: 34px;
}

.brand .brand-sub {
  display: block;
  font-size: 0.68rem;
  font-weight: 500;
  color: var(--color-ink-faint);
  letter-spacing: 0.03em;
}

.main-nav {
  display: flex;
  align-items: center;
  gap: 4px;
  flex-wrap: wrap;
}

.main-nav a {
  color: var(--color-ink);
  font-size: 0.94rem;
  font-weight: 600;
  padding: 8px 12px;
  border-radius: var(--radius-sm);
  text-decoration: none;
  white-space: nowrap;
}

.main-nav a:hover {
  background: var(--color-deep-blue-tint);
  color: var(--color-deep-blue);
}

.main-nav a[aria-current="page"] {
  background: var(--color-deep-blue);
  color: #fff;
}

.nav-toggle {
  display: none;
  width: 40px;
  height: 40px;
  border: 1px solid var(--color-border-strong);
  border-radius: var(--radius-sm);
  background: var(--color-surface);
  cursor: pointer;
  flex-shrink: 0;
  position: relative;
}

.nav-toggle span,
.nav-toggle span::before,
.nav-toggle span::after {
  content: "";
  position: absolute;
  left: 9px;
  right: 9px;
  height: 2px;
  background: var(--color-ink);
  transition: transform 0.2s ease, opacity 0.2s ease;
}

.nav-toggle span { top: 19px; }
.nav-toggle span::before { top: -7px; }
.nav-toggle span::after { top: 7px; }

.nav-toggle[aria-expanded="true"] span { background: transparent; }
.nav-toggle[aria-expanded="true"] span::before { transform: translateY(7px) rotate(45deg); }
.nav-toggle[aria-expanded="true"] span::after { transform: translateY(-7px) rotate(-45deg); }

@media (max-width: 900px) {
  .nav-toggle { display: block; }
  .main-nav {
    position: fixed;
    top: var(--header-h);
    left: 0;
    right: 0;
    background: var(--color-surface);
    border-bottom: 1px solid var(--color-border);
    flex-direction: column;
    align-items: stretch;
    gap: 0;
    max-height: 0;
    overflow: hidden;
    transition: max-height 0.25s ease;
    box-shadow: var(--shadow-md);
  }
  .main-nav.is-open { max-height: 480px; }
  .main-nav a {
    padding: 14px 20px;
    border-bottom: 1px solid var(--color-border);
    border-radius: 0;
  }
}

/* ---------- 5. Hero ---------- */
.hero {
  padding: 52px 0 40px;
  background: linear-gradient(180deg, var(--color-deep-blue-tint) 0%, var(--color-bg) 100%);
}

.hero .container {
  display: grid;
  grid-template-columns: 1.15fr 0.85fr;
  gap: 40px;
  align-items: center;
}

@media (max-width: 900px) {
  .hero .container { grid-template-columns: 1fr; }
}

.hero-kicker {
  display: inline-flex;
  align-items: center;
  gap: 8px;
  background: var(--color-surface);
  border: 1px solid var(--color-border-strong);
  color: var(--color-edu-cyan);
  font-size: 0.82rem;
  font-weight: 700;
  padding: 6px 12px;
  border-radius: 999px;
  margin-bottom: 16px;
}

.hero h1 {
  font-size: clamp(1.6rem, 3.4vw, 2.35rem);
  margin-bottom: 18px;
}

.hero .lede {
  color: var(--color-ink-soft);
  font-size: 1.02rem;
  max-width: 60ch;
}

.hero-actions {
  display: flex;
  gap: 12px;
  margin-top: 22px;
  flex-wrap: wrap;
}

.hero-figure {
  background: var(--color-surface);
  border: 1px solid var(--color-border);
  border-radius: var(--radius-lg);
  padding: 18px;
  box-shadow: var(--shadow-md);
}

.hero-stat-row {
  display: flex;
  gap: 18px;
  margin-top: 26px;
  flex-wrap: wrap;
}

.hero-stat {
  border-left: 3px solid var(--color-edu-cyan);
  padding-left: 10px;
}

.hero-stat b {
  display: block;
  color: var(--color-deep-blue);
  font-size: 1.05rem;
}

.hero-stat span {
  font-size: 0.82rem;
  color: var(--color-ink-faint);
}

/* ---------- 6. 按钮 Buttons ---------- */
.btn {
  display: inline-flex;
  align-items: center;
  gap: 8px;
  padding: 11px 20px;
  border-radius: var(--radius-sm);
  font-weight: 700;
  font-size: 0.95rem;
  border: 1px solid transparent;
  cursor: pointer;
  text-decoration: none;
}

.btn:hover { text-decoration: none; }

.btn-primary {
  background: var(--color-deep-blue);
  color: #fff;
}
.btn-primary:hover { background: var(--color-deep-blue-2); }

.btn-outline {
  background: var(--color-surface);
  color: var(--color-deep-blue);
  border-color: var(--color-border-strong);
}
.btn-outline:hover { border-color: var(--color-deep-blue); }

.btn-ghost {
  background: transparent;
  color: var(--color-deep-blue-2);
  padding: 11px 6px;
}

.btn-sm { padding: 7px 14px; font-size: 0.85rem; }

/* ---------- 7. 标签 Tags / Badges ---------- */
.tag {
  display: inline-block;
  font-size: 0.74rem;
  font-weight: 700;
  padding: 3px 9px;
  border-radius: 999px;
  letter-spacing: 0.02em;
}

.tag-cat { background: var(--color-deep-blue-tint); color: var(--color-deep-blue); }
.tag-cyan { background: var(--color-edu-cyan-tint); color: var(--color-edu-cyan); }
.tag-green { background: var(--color-sport-green-tint); color: var(--color-sport-green); }
.tag-orange { background: var(--color-accent-orange-tint); color: var(--color-accent-orange); }

.tag-type {
  display: inline-flex;
  align-items: center;
  gap: 5px;
  font-size: 0.72rem;
  font-weight: 700;
  padding: 2px 9px;
  border-radius: 5px;
  border: 1px solid currentColor;
}
.tag-type::before {
  content: "";
  width: 6px;
  height: 6px;
  border-radius: 50%;
  background: currentColor;
}
.tag-type--fact { color: var(--color-fact); }
.tag-type--interpretation { color: var(--color-interpretation); }
.tag-type--example { color: var(--color-example); }
.tag-type--opinion { color: var(--color-opinion); }

.meta-row {
  display: flex;
  align-items: center;
  gap: 10px;
  flex-wrap: wrap;
  font-size: 0.82rem;
  color: var(--color-ink-faint);
  margin-bottom: 10px;
}

/* ---------- 8. 卡片 Cards ---------- */
.card {
  background: var(--color-surface);
  border: 1px solid var(--color-border);
  border-radius: var(--radius-md);
  padding: 22px;
  box-shadow: var(--shadow-sm);
}

.card-hover:hover {
  box-shadow: var(--shadow-md);
  border-color: var(--color-border-strong);
}

.summary-card h3 {
  font-size: 1.02rem;
  margin-bottom: 8px;
}

.summary-card p {
  color: var(--color-ink-soft);
  font-size: 0.92rem;
  margin-bottom: 10px;
}

.summary-card .link-more {
  font-size: 0.86rem;
  font-weight: 700;
}

/* ---------- 9. 长文章 Article ---------- */
.article {
  background: var(--color-surface);
  border: 1px solid var(--color-border);
  border-radius: var(--radius-lg);
  padding: 32px clamp(18px, 4vw, 40px);
  margin-bottom: 40px;
}

.article-head {
  border-bottom: 1px dashed var(--color-border-strong);
  padding-bottom: 18px;
  margin-bottom: 20px;
}

.article-head h2 {
  font-size: clamp(1.25rem, 2.4vw, 1.55rem);
}

.article-figure {
  margin: 20px 0;
  text-align: center;
  background: var(--color-bg-alt);
  border: 1px solid var(--color-border);
  border-radius: var(--radius-md);
  padding: 16px;
}

.article-figure figcaption {
  margin-top: 10px;
  font-size: 0.84rem;
  color: var(--color-ink-faint);
}

.article-body h3 {
  margin-top: 1.6em;
}

.callout {
  background: var(--color-edu-cyan-tint);
  border-left: 4px solid var(--color-edu-cyan);
  border-radius: var(--radius-sm);
  padding: 14px 18px;
  margin: 20px 0;
  font-size: 0.95rem;
  color: var(--color-ink);
}

.callout-orange {
  background: var(--color-accent-orange-tint);
  border-left-color: var(--color-accent-orange);
}

.source-box {
  margin-top: 18px;
  background: var(--color-bg-alt);
  border: 1px solid var(--color-border);
  border-radius: var(--radius-sm);
  padding: 14px 18px;
  font-size: 0.88rem;
  color: var(--color-ink-soft);
}

.source-box dt { font-weight: 700; color: var(--color-deep-blue); margin-top: 8px; }
.source-box dt:first-child { margin-top: 0; }
.source-box dd { margin: 2px 0 0; }

.article-links {
  margin-top: 16px;
  display: flex;
  flex-wrap: wrap;
  gap: 10px 18px;
  font-size: 0.9rem;
}

/* ---------- 10. 版本 / 来源 模块 ---------- */
.version-panel {
  background: var(--color-surface);
  border: 1px solid var(--color-border);
  border-radius: var(--radius-lg);
  padding: 24px;
  box-shadow: var(--shadow-sm);
}

.version-tabs {
  display: flex;
  gap: 8px;
  flex-wrap: wrap;
  margin-bottom: 18px;
  border-bottom: 1px solid var(--color-border);
  padding-bottom: 12px;
}

.version-tab {
  background: var(--color-bg-alt);
  border: 1px solid var(--color-border-strong);
  color: var(--color-ink-soft);
  padding: 8px 14px;
  border-radius: 999px;
  font-size: 0.86rem;
  font-weight: 700;
  cursor: pointer;
}

.version-tab.is-active {
  background: var(--color-deep-blue);
  border-color: var(--color-deep-blue);
  color: #fff;
}

.version-pane { display: none; }
.version-pane.is-active { display: block; }

.version-grid {
  display: grid;
  grid-template-columns: repeat(auto-fit, minmax(220px, 1fr));
  gap: 14px;
  margin-top: 14px;
}

.version-fact {
  background: var(--color-bg-alt);
  border-radius: var(--radius-sm);
  padding: 12px 14px;
  font-size: 0.88rem;
}
.version-fact b { display: block; color: var(--color-deep-blue); font-size: 0.82rem; margin-bottom: 4px; }

/* ---------- 11. Tabs（战术图等） ---------- */
.tabs {
  display: flex;
  gap: 8px;
  flex-wrap: wrap;
  margin-bottom: 16px;
}

.tab-btn {
  background: var(--color-surface);
  border: 1px solid var(--color-border-strong);
  padding: 9px 16px;
  border-radius: var(--radius-sm);
  font-weight: 700;
  font-size: 0.88rem;
  cursor: pointer;
  color: var(--color-ink);
}

.tab-btn.is-active {
  background: var(--color-sport-green);
  border-color: var(--color-sport-green);
  color: #fff;
}

.tab-panel { display: none; }
.tab-panel.is-active { display: grid; grid-template-columns: 1fr 1fr; gap: 20px; align-items: center; }

@media (max-width: 760px) {
  .tab-panel.is-active { grid-template-columns: 1fr; }
}

.tab-panel .panel-figure {
  background: var(--color-bg-alt);
  border: 1px solid var(--color-border);
  border-radius: var(--radius-md);
  padding: 14px;
}

/* ---------- 12. 时间线 Timeline ---------- */
.timeline {
  position: relative;
  padding-left: 28px;
  border-left: 2px solid var(--color-border-strong);
}

.timeline-item {
  position: relative;
  padding-bottom: 26px;
}

.timeline-item::before {
  content: "";
  position: absolute;
  left: -34px;
  top: 4px;
  width: 12px;
  height: 12px;
  border-radius: 50%;
  background: var(--color-edu-cyan);
  border: 2px solid var(--color-surface);
  box-shadow: 0 0 0 2px var(--color-edu-cyan);
}

.timeline-item .t-year {
  font-weight: 700;
  color: var(--color-deep-blue);
  font-size: 0.95rem;
}

.timeline-item h4 { margin: 4px 0 6px; }
.timeline-item p { color: var(--color-ink-soft); font-size: 0.92rem; margin-bottom: 4px; }

/* ---------- 13. FAQ ---------- */
.faq-list {
  display: flex;
  flex-direction: column;
  gap: 10px;
}

.faq-item {
  background: var(--color-surface);
  border: 1px solid var(--color-border);
  border-radius: var(--radius-md);
  overflow: hidden;
}

.faq-q {
  width: 100%;
  text-align: left;
  background: none;
  border: none;
  padding: 15px 46px 15px 18px;
  font-weight: 700;
  font-size: 0.96rem;
  color: var(--color-ink);
  cursor: pointer;
  position: relative;
}

.faq-q::after {
  content: "+";
  position: absolute;
  right: 16px;
  top: 50%;
  transform: translateY(-50%);
  font-size: 1.3rem;
  color: var(--color-edu-cyan);
  font-weight: 400;
}

.faq-item.is-open .faq-q::after { content: "\2212"; }

.faq-a {
  max-height: 0;
  overflow: hidden;
  padding: 0 18px;
  color: var(--color-ink-soft);
  font-size: 0.92rem;
  transition: max-height 0.25s ease, padding 0.2s ease;
}

.faq-item.is-open .faq-a {
  max-height: 600px;
  padding: 0 18px 16px;
}

/* ---------- 14. 互动题 / AI问答演示 ---------- */
.quiz-demo {
  background: var(--color-surface);
  border: 1px solid var(--color-border);
  border-radius: var(--radius-lg);
  padding: 22px;
}

.quiz-q { font-weight: 700; margin-bottom: 14px; }

.quiz-options {
  display: grid;
  gap: 10px;
  margin-bottom: 14px;
}

.quiz-opt {
  text-align: left;
  background: var(--color-bg-alt);
  border: 1px solid var(--color-border-strong);
  padding: 10px 14px;
  border-radius: var(--radius-sm);
  cursor: pointer;
  font-size: 0.92rem;
  color: var(--color-ink);
}

.quiz-opt.is-correct { background: var(--color-sport-green-tint); border-color: var(--color-sport-green); }
.quiz-opt.is-wrong { background: var(--color-accent-orange-tint); border-color: var(--color-accent-orange); }

.quiz-feedback {
  font-size: 0.9rem;
  padding: 12px 14px;
  border-radius: var(--radius-sm);
  background: var(--color-edu-cyan-tint);
  color: var(--color-ink);
  display: none;
}
.quiz-feedback.is-visible { display: block; }

.ai-demo {
  background: var(--color-surface);
  border: 1px solid var(--color-border);
  border-radius: var(--radius-lg);
  padding: 20px;
}

.ai-demo-qs {
  display: flex;
  flex-wrap: wrap;
  gap: 8px;
  margin-bottom: 16px;
}

.ai-demo-q-btn {
  background: var(--color-deep-blue-tint);
  border: 1px solid var(--color-border-strong);
  color: var(--color-deep-blue);
  padding: 8px 14px;
  border-radius: 999px;
  font-size: 0.85rem;
  font-weight: 700;
  cursor: pointer;
}

.ai-demo-q-btn.is-active { background: var(--color-deep-blue); color: #fff; }

.ai-demo-answer { display: none; border-top: 1px dashed var(--color-border-strong); padding-top: 14px; }
.ai-demo-answer.is-active { display: block; }

.ai-demo-answer .a-source {
  margin-top: 12px;
  font-size: 0.84rem;
  color: var(--color-ink-faint);
  background: var(--color-bg-alt);
  padding: 8px 12px;
  border-radius: var(--radius-sm);
}

/* ---------- 15. 手机 App 界面示意 ---------- */
.phone-mock {
  width: 220px;
  margin: 0 auto;
}

.phone-mock-row {
  display: flex;
  gap: 22px;
  flex-wrap: wrap;
  justify-content: center;
}

/* ---------- 16. 知识图谱 / 流程图容器 ---------- */
.diagram-box {
  background: var(--color-surface);
  border: 1px solid var(--color-border);
  border-radius: var(--radius-lg);
  padding: 20px;
  box-shadow: var(--shadow-sm);
  overflow-x: auto;
}

.diagram-box figcaption {
  margin-top: 12px;
  font-size: 0.85rem;
  color: var(--color-ink-faint);
  text-align: center;
}

/* ---------- 17. 表格 ---------- */
.table-wrap { overflow-x: auto; margin: 18px 0; border: 1px solid var(--color-border); border-radius: var(--radius-md); }

table.data-table { min-width: 480px; }
.data-table th, .data-table td {
  text-align: left;
  padding: 10px 14px;
  border-bottom: 1px solid var(--color-border);
  font-size: 0.9rem;
}
.data-table th { background: var(--color-bg-alt); color: var(--color-deep-blue); }
.data-table tr:last-child td { border-bottom: none; }

/* ---------- 18. 面包屑 ---------- */
.breadcrumb {
  font-size: 0.82rem;
  color: var(--color-ink-faint);
  padding: 14px 0;
}
.breadcrumb a { color: var(--color-ink-soft); }
.breadcrumb .sep { margin: 0 6px; }
.breadcrumb .current { color: var(--color-ink); font-weight: 600; }

/* ---------- 19. 免责声明 ---------- */
.disclaimer {
  font-size: 0.82rem;
  color: var(--color-ink-faint);
  background: var(--color-bg-alt);
  border: 1px dashed var(--color-border-strong);
  border-radius: var(--radius-md);
  padding: 14px 18px;
  margin: 20px 0;
}

.plan-badge {
  display: inline-block;
  background: var(--color-accent-orange-tint);
  color: var(--color-accent-orange);
  font-weight: 700;
  font-size: 0.76rem;
  padding: 3px 10px;
  border-radius: 999px;
  margin-bottom: 10px;
}

/* ---------- 20. 页脚 Footer ---------- */
.site-footer {
  background: var(--color-deep-blue);
  color: #d8e2f0;
  padding: 48px 0 26px;
  margin-top: 40px;
}

.site-footer a { color: #eaf1fb; }
.site-footer h4 { color: #fff; font-size: 0.95rem; }

.footer-grid {
  display: grid;
  grid-template-columns: 1.4fr 1fr 1fr 1.2fr;
  gap: 30px;
}

@media (max-width: 860px) {
  .footer-grid { grid-template-columns: 1fr 1fr; }
}
@media (max-width: 520px) {
  .footer-grid { grid-template-columns: 1fr; }
}

.footer-grid ul { list-style: none; padding: 0; margin: 0; }
.footer-grid li { margin-bottom: 8px; font-size: 0.88rem; }

.footer-brand p {
  color: #b9c7dd;
  font-size: 0.88rem;
  max-width: 40ch;
}

.footer-bottom {
  border-top: 1px solid rgba(255,255,255,0.14);
  margin-top: 32px;
  padding-top: 18px;
  font-size: 0.78rem;
  color: #9fb0c8;
  display: flex;
  justify-content: space-between;
  flex-wrap: wrap;
  gap: 10px;
}

.footer-disclaimer {
  font-size: 0.76rem;
  color: #8fa1bb;
  margin-top: 14px;
  max-width: 90ch;
  line-height: 1.7;
}

/* ---------- 21. 返回顶部 ---------- */
.back-to-top {
  position: fixed;
  right: 20px;
  bottom: 24px;
  width: 44px;
  height: 44px;
  border-radius: 50%;
  background: var(--color-deep-blue);
  color: #fff;
  border: none;
  cursor: pointer;
  display: none;
  align-items: center;
  justify-content: center;
  box-shadow: var(--shadow-md);
  z-index: 90;
  font-size: 1.1rem;
}

.back-to-top.is-visible { display: flex; }

/* ---------- 22. 学习进度示意 ---------- */
.progress-list { display: flex; flex-direction: column; gap: 12px; }
.progress-row { display: flex; align-items: center; gap: 12px; }
.progress-row .p-label { width: 140px; font-size: 0.86rem; color: var(--color-ink-soft); flex-shrink: 0; }
.progress-track { flex: 1; height: 10px; border-radius: 999px; background: var(--color-bg-alt); overflow: hidden; }
.progress-fill { height: 100%; border-radius: 999px; background: var(--color-edu-cyan); }
.progress-row .p-state { width: 74px; font-size: 0.78rem; text-align: right; color: var(--color-ink-faint); flex-shrink: 0; }

/* ---------- 23. 分类导航条（首页知识图谱下方） ---------- */
.pillar-nav {
  display: grid;
  grid-template-columns: repeat(4, 1fr);
  gap: 16px;
}
@media (max-width: 760px) { .pillar-nav { grid-template-columns: repeat(2, 1fr); } }

.pillar-card {
  background: var(--color-surface);
  border: 1px solid var(--color-border);
  border-radius: var(--radius-md);
  padding: 18px;
  text-align: left;
}
.pillar-card img { width: 40px; height: 40px; margin-bottom: 10px; }
.pillar-card h4 { margin-bottom: 6px; font-size: 0.98rem; }
.pillar-card p { font-size: 0.84rem; color: var(--color-ink-soft); margin: 0; }

/* ---------- 24. 工具类 ---------- */
.text-center { text-align: center; }
.mt-0 { margin-top: 0; }
.mb-0 { margin-bottom: 0; }
.small { font-size: 0.85rem; color: var(--color-ink-soft); }
.hr-soft { border: none; border-top: 1px dashed var(--color-border-strong); margin: 30px 0; }
.sr-only {
  position: absolute;
  width: 1px; height: 1px;
  padding: 0; margin: -1px;
  overflow: hidden;
  clip: rect(0,0,0,0);
  white-space: nowrap; border: 0;
}
.skip-link {
  position: absolute;
  left: -999px;
  top: 0;
  background: var(--color-deep-blue);
  color: #fff;
  padding: 10px 16px;
  z-index: 200;
}
.skip-link:focus { left: 10px; top: 10px; }

/* ---------- 25. 响应式细节 ---------- */
@media (max-width: 480px) {
  body { font-size: 15px; }
  .section { padding: 40px 0; }
  .article { padding: 24px 16px; }
  h1 { font-size: 1.5rem; }
  h2 { font-size: 1.25rem; }
  .footer-bottom { flex-direction: column; }
}