/* ============================================================
   ChatGPT Foundations for Teachers · 教师中文学习版
   风格体系参照 club.smartschool.chat：
   主色 orange #f97316 / 辅色 teal #0f766e / 深墨 #111827
   奶油底 #fff7ed / 玻璃拟态卡片 / 圆角 / 柔和阴影
   ============================================================ */
:root {
  --brand-primary: #f97316;
  --brand-primary-dark: #ea580c;
  --brand-secondary: #0f766e;
  --brand-dark: #111827;
  --brand-sky: #0ea5e9;
  --brand-amber: #fbbf24;
  --surface-base: #fffdf8;
  --surface-cream: #fff7ed;
  --surface-cyan: #ecfeff;
  --surface-soft: #f8fafc;
  --ink: #1f2937;
  --ink-soft: #6b7280;
  --border: hsla(20, 6%, 90%, 1);
  --glass-bg: hsla(0, 0%, 100%, .55);
  --glass-bg-strong: hsla(0, 0%, 100%, .75);
  --glass-border: hsla(0, 0%, 100%, .65);
  --glass-blur: blur(16px) saturate(180%);
  --radius: 18px;
  --radius-sm: 12px;
  --shadow-soft: 0 8px 30px rgba(17, 24, 39, .07);
  --shadow-lift: 0 16px 48px rgba(17, 24, 39, .13);
  --font-sans: "Plus Jakarta Sans", "PingFang SC", "Hiragino Sans GB", "Microsoft YaHei", "Noto Sans SC", system-ui, -apple-system, sans-serif;
  --font-mono: "JetBrains Mono", ui-monospace, SFMono-Regular, Menlo, monospace;
}
* { box-sizing: border-box; margin: 0; padding: 0; }
html { scroll-behavior: smooth; }
body {
  font-family: var(--font-sans);
  color: var(--ink);
  background:
    radial-gradient(900px 480px at 85% -80px, rgba(14, 165, 233, .13), transparent 60%),
    radial-gradient(1100px 560px at -10% -120px, rgba(249, 115, 22, .16), transparent 55%),
    linear-gradient(180deg, var(--surface-cream) 0%, var(--surface-base) 34%, var(--surface-base) 100%);
  min-height: 100vh;
  line-height: 1.65;
  -webkit-font-smoothing: antialiased;
}
a { color: inherit; text-decoration: none; }
img { max-width: 100%; display: block; }
.container { width: min(1120px, calc(100% - 48px)); margin: 0 auto; }
.mono { font-family: var(--font-mono); }

/* ---------- 顶部导航（玻璃拟态 + OpenAI 课程字标） ---------- */
.site-header {
  position: sticky; top: 0; z-index: 50;
  backdrop-filter: var(--glass-blur);
  -webkit-backdrop-filter: var(--glass-blur);
  background: var(--glass-bg-strong);
  border-bottom: 1px solid var(--border);
}
.nav { display: flex; align-items: center; gap: 16px; height: 64px; }
.course-brand { display: flex; align-items: center; gap: 13px; min-width: 0; }
.org-mark {
  font-size: 19px; font-weight: 800; color: var(--brand-dark);
  letter-spacing: -.04em; display: flex; align-items: center; gap: 1px; white-space: nowrap;
}
.org-mark .dot1, .org-mark .dot2 { width: 7px; height: 7px; border-radius: 50%; margin-left: 3px; }
.org-mark .dot1 { background: var(--brand-primary); }
.org-mark .dot2 { background: var(--brand-secondary); }
.course-brand .divider { width: 1px; height: 26px; background: var(--border); }
.course-title { display: flex; flex-direction: column; min-width: 0; }
.course-title b {
  font-size: 14.5px; font-weight: 800; color: var(--brand-dark); letter-spacing: -.01em;
  white-space: nowrap; overflow: hidden; text-overflow: ellipsis;
}
.course-title small { font-size: 10.5px; font-weight: 600; color: var(--ink-soft); letter-spacing: .1em; }
.nav-links { display: flex; gap: 4px; margin-left: auto; align-items: center; }
.nav-links a {
  padding: 7px 16px; border-radius: 999px; font-size: 14px; font-weight: 600; color: #c2410c;
  border: 1.5px solid #fdba74; background: transparent;
  transition: all .18s ease;
}
.nav-links a:hover { border-color: var(--brand-primary); color: var(--brand-primary-dark); background: #fff7ed; }
.nav-links a.active { border-color: var(--brand-primary); border-width: 2px; color: var(--brand-primary-dark); font-weight: 800; padding: 6.5px 15px; }
.btn {
  display: inline-flex; align-items: center; gap: 8px; border: none; cursor: pointer;
  padding: 12px 22px; border-radius: 999px; font-size: 15px; font-weight: 700; font-family: inherit;
  transition: all .2s ease;
}
.btn-primary {
  background: linear-gradient(135deg, var(--brand-primary), #fb923c); color: #fff;
  box-shadow: 0 10px 24px rgba(249, 115, 22, .35);
}
.btn-primary:hover { transform: translateY(-2px); box-shadow: 0 14px 32px rgba(249, 115, 22, .45); }
.btn-ghost { background: transparent; color: var(--brand-dark); border: 1.5px solid var(--border); }
.btn-ghost:hover { border-color: var(--brand-dark); }
.btn-sm { padding: 8px 16px; font-size: 13px; }

/* ---------- Hero ---------- */
.hero { padding: 84px 0 56px; display: grid; grid-template-columns: 1.15fr .85fr; gap: 48px; align-items: center; }
.hero-badge {
  display: inline-flex; align-items: center; gap: 8px;
  background: #fff; border: 1px solid var(--border); border-radius: 999px;
  padding: 7px 16px; font-size: 13px; font-weight: 600; color: var(--brand-secondary);
  box-shadow: var(--shadow-soft); margin-bottom: 22px;
}
.hero-badge .dot { width: 8px; height: 8px; border-radius: 50%; background: var(--brand-primary); }
.hero h1 { font-size: clamp(34px, 5vw, 52px); line-height: 1.14; font-weight: 800; color: var(--brand-dark); letter-spacing: -.02em; }
.hero h1 .accent { background: linear-gradient(120deg, var(--brand-primary), #f59e0b); -webkit-background-clip: text; background-clip: text; color: transparent; }
.hero p.lead { margin: 20px 0 30px; font-size: 17px; color: #4b5563; max-width: 34em; }
.hero-cta { display: flex; gap: 14px; flex-wrap: wrap; align-items: center; }
.hero-meta { display: flex; gap: 26px; margin-top: 34px; flex-wrap: wrap; }
.hero-meta .stat { display: flex; flex-direction: column; }
.hero-meta .stat b { font-size: 22px; font-weight: 800; color: var(--brand-dark); }
.hero-meta .stat span { font-size: 12.5px; color: var(--ink-soft); }
.hero-visual { position: relative; }
.card-float {
  border-radius: var(--radius); overflow: hidden; box-shadow: var(--shadow-lift);
  border: 1px solid var(--glass-border); background: #fff;
}
.hero-visual img { width: 100%; height: 100%; object-fit: cover; aspect-ratio: 16/10.5; }
.float-chip {
  position: absolute; display: flex; align-items: center; gap: 10px;
  background: var(--glass-bg-strong); backdrop-filter: var(--glass-blur);
  border: 1px solid var(--glass-border); border-radius: 14px;
  padding: 10px 16px; font-size: 13px; font-weight: 700; color: var(--brand-dark);
  box-shadow: var(--shadow-soft);
}
.float-chip .ico { width: 30px; height: 30px; border-radius: 9px; display: grid; place-items: center; background: rgba(15, 118, 110, .12); }
.chip-a { top: -18px; right: 22px; }
.chip-b { bottom: -16px; left: -14px; }

/* ---------- 区块通用 ---------- */
section.block { padding: 64px 0; }
.block-head { max-width: 640px; margin-bottom: 36px; }
.block-head .kicker { font-family: var(--font-mono); font-size: 12.5px; font-weight: 700; color: var(--brand-primary-dark); letter-spacing: .16em; text-transform: uppercase; margin-bottom: 10px; }
.block-head h2 { font-size: clamp(24px, 3.4vw, 34px); font-weight: 800; color: var(--brand-dark); letter-spacing: -.01em; line-height: 1.25; }
.block-head p { margin-top: 12px; color: #4b5563; font-size: 15.5px; }

/* ---------- 编号特性卡 01/02/03/04 ---------- */
.feature-grid { display: grid; grid-template-columns: repeat(4, 1fr); gap: 18px; }
.feature-card {
  background: var(--glass-bg); backdrop-filter: var(--glass-blur);
  border: 1px solid var(--glass-border); border-radius: var(--radius);
  padding: 26px 22px; transition: all .22s ease; position: relative; overflow: hidden;
}
.feature-card:hover { transform: translateY(-4px); box-shadow: var(--shadow-lift); }
.feature-card .num {
  font-family: var(--font-mono); font-size: 13px; font-weight: 700;
  color: var(--brand-primary); background: rgba(249, 115, 22, .1);
  border-radius: 8px; padding: 3px 9px; display: inline-block; margin-bottom: 14px;
}
.feature-card h3 { font-size: 16.5px; font-weight: 800; color: var(--brand-dark); margin-bottom: 8px; }
.feature-card p { font-size: 13.8px; color: #4b5563; }

/* ---------- 模块卡 ---------- */
.module-grid { display: grid; grid-template-columns: repeat(3, 1fr); gap: 18px; }
.module-card {
  background: #fff; border: 1px solid var(--border); border-radius: var(--radius);
  padding: 24px; display: flex; flex-direction: column; gap: 12px;
  transition: all .22s ease; position: relative;
}
.module-card:hover { transform: translateY(-4px); box-shadow: var(--shadow-lift); border-color: rgba(249, 115, 22, .45); }
.module-card .top { display: flex; align-items: center; justify-content: space-between; }
.module-card .icon {
  width: 46px; height: 46px; border-radius: 14px; display: grid; place-items: center; font-size: 22px;
  background: linear-gradient(135deg, var(--surface-cream), #ffedd5); border: 1px solid #fed7aa;
}
.module-card .tag {
  font-family: var(--font-mono); font-size: 12px; font-weight: 700; color: var(--ink-soft);
}
.module-card h3 { font-size: 17px; font-weight: 800; color: var(--brand-dark); line-height: 1.35; }
.module-card .en { font-size: 12.5px; color: var(--ink-soft); font-weight: 600; margin-top: -8px; }
.module-card p { font-size: 13.8px; color: #4b5563; flex: 1; }
.module-card .meta { display: flex; gap: 14px; font-size: 12.5px; color: var(--ink-soft); font-weight: 600; }
.module-card .go { margin-top: 4px; color: var(--brand-primary-dark); font-weight: 700; font-size: 14px; }

/* ---------- 深色工具带 ---------- */
.tool-band { background: var(--brand-dark); border-radius: 24px; padding: 48px; color: #fff; position: relative; overflow: hidden; }
.tool-band::after { content: ""; position: absolute; inset: 0; background: radial-gradient(600px 300px at 90% -40%, rgba(249, 115, 22, .35), transparent 60%); pointer-events: none; }
.tool-band h2 { font-size: clamp(22px, 3vw, 30px); font-weight: 800; margin-bottom: 10px; position: relative; }
.tool-band > p { color: rgba(255, 255, 255, .72); margin-bottom: 30px; max-width: 46em; position: relative; }
.tool-grid { display: grid; grid-template-columns: repeat(4, 1fr); gap: 16px; position: relative; }
.tool-item { background: rgba(255, 255, 255, .06); border: 1px solid rgba(255, 255, 255, .14); border-radius: 16px; padding: 22px 18px; backdrop-filter: blur(6px); }
.tool-item .ico { font-size: 24px; margin-bottom: 12px; }
.tool-item h3 { font-size: 15.5px; font-weight: 700; margin-bottom: 6px; }
.tool-item p { font-size: 13px; color: rgba(255, 255, 255, .66); }

/* ---------- FAQ ---------- */
.faq-list { display: grid; gap: 12px; max-width: 760px; }
details.faq { background: #fff; border: 1px solid var(--border); border-radius: var(--radius-sm); padding: 18px 22px; }
details.faq summary { cursor: pointer; font-weight: 700; color: var(--brand-dark); font-size: 15px; list-style: none; display: flex; justify-content: space-between; align-items: center; }
details.faq summary::after { content: "+"; font-family: var(--font-mono); font-size: 18px; color: var(--brand-primary); }
details.faq[open] summary::after { content: "−"; }
details.faq p { margin-top: 10px; color: #4b5563; font-size: 14.5px; }

/* ---------- 页脚 ---------- */
.site-footer { border-top: 1px solid var(--border); background: var(--surface-base); padding: 36px 0 44px; margin-top: 40px; }
.footer-row { display: flex; justify-content: space-between; align-items: center; gap: 24px; flex-wrap: wrap; }
.site-footer .note { font-size: 12px; color: #9ca3af; max-width: 64em; line-height: 1.7; }
.site-footer .note a { color: var(--ink-soft); text-decoration: underline; text-underline-offset: 3px; }

/* ---------- 课程页 ---------- */
.page-hero { padding: 56px 0 36px; }
.crumb { font-size: 13px; color: var(--ink-soft); font-weight: 600; margin-bottom: 14px; display: flex; gap: 8px; align-items: center; }
.crumb a:hover { color: var(--brand-primary-dark); }
.page-hero h1 { font-size: clamp(28px, 4vw, 42px); font-weight: 800; color: var(--brand-dark); letter-spacing: -.015em; }
.page-hero .sub { margin-top: 10px; color: #4b5563; font-size: 16px; max-width: 46em; }
.pill-row { display: flex; gap: 10px; margin-top: 20px; flex-wrap: wrap; }
.pill { background: #fff; border: 1px solid var(--border); border-radius: 999px; padding: 7px 15px; font-size: 13px; font-weight: 700; color: #374151; }
.pill.warn { border-color: #fde68a; background: #fffbeb; color: #92400e; }

.accordion { display: grid; gap: 16px; }
.acc-item { background: #fff; border: 1px solid var(--border); border-radius: var(--radius); overflow: hidden; transition: box-shadow .2s; }
.acc-item:hover { box-shadow: var(--shadow-soft); }
.acc-head { display: flex; gap: 18px; align-items: center; padding: 22px 24px; cursor: pointer; user-select: none; }
.acc-head .icon { width: 48px; height: 48px; border-radius: 14px; display: grid; place-items: center; font-size: 23px; background: linear-gradient(135deg, var(--surface-cream), #ffedd5); border: 1px solid #fed7aa; flex: none; }
.acc-head .titles { flex: 1; }
.acc-head h3 { font-size: 18px; font-weight: 800; color: var(--brand-dark); }
.acc-head .titles .en { font-size: 13px; color: var(--ink-soft); font-weight: 600; }
.acc-head .info { font-size: 12.5px; color: var(--ink-soft); font-weight: 700; text-align: right; }
.acc-head .chev { color: var(--brand-primary); font-size: 20px; transition: transform .2s; }
.acc-item.open .chev { transform: rotate(90deg); }
.acc-body { display: none; border-top: 1px solid var(--border); background: var(--surface-soft); }
.acc-item.open .acc-body { display: block; }
.lesson-row { display: flex; align-items: center; gap: 14px; padding: 13px 26px; border-bottom: 1px solid #eef0f3; transition: background .15s; }
.lesson-row:last-child { border-bottom: none; }
.lesson-row:hover { background: #fff; }
.lesson-row .no { font-family: var(--font-mono); font-size: 12px; color: #9ca3af; width: 26px; flex: none; }
.lesson-row .name { flex: 1; font-size: 14.5px; font-weight: 600; color: #1f2937; }
.lesson-row .name small { display: block; font-weight: 500; color: #9ca3af; font-size: 12px; }
.badge { font-size: 11.5px; font-weight: 700; padding: 3px 10px; border-radius: 999px; white-space: nowrap; }
.badge.video { background: #fee2e2; color: #b91c1c; }
.badge.reading { background: #dbeafe; color: #1d4ed8; }
.badge.tip { background: #fef3c7; color: #b45309; }
.badge.activity { background: #d1fae5; color: #047857; }
.badge.demo { background: #ede9fe; color: #6d28d9; }
.badge.quiz, .badge.assessment { background: #ffe4e6; color: #be123c; }
.badge.scenario { background: #fff7ed; color: #c2410c; border: 1px solid #fed7aa; }
.badge.survey { background: #e0f2fe; color: #0369a1; }
.badge.summary, .badge.overview { background: #f1f5f9; color: #475569; }
.lesson-row .mins { font-size: 12px; color: #9ca3af; font-weight: 600; width: 52px; text-align: right; }
.lesson-row .done-mark { color: var(--brand-secondary); font-weight: 800; }

/* ---------- 学习页 ---------- */
.lesson-layout { display: grid; grid-template-columns: 290px 1fr; gap: 32px; padding-bottom: 64px; }
.lesson-side { position: sticky; top: 88px; align-self: start; max-height: calc(100vh - 110px); overflow-y: auto; border-radius: var(--radius); background: #fff; border: 1px solid var(--border); padding: 14px 12px 16px; scrollbar-width: thin; }
.side-head { font-size: 12px; letter-spacing: .16em; color: var(--ink-soft); font-weight: 800; padding: 2px 10px 12px; }
/* 模块根节点（手风琴，默认收起） */
.side-mod { border: 1px solid var(--border); border-radius: 14px; margin: 0 0 10px; overflow: hidden; background: #fff; transition: border-color .2s, box-shadow .2s; }
.side-mod.open { border-color: #fdba74; background: linear-gradient(180deg, #fffaf3, #fff 60%); box-shadow: 0 8px 20px -12px rgba(249, 115, 22, .38); }
.side-mod-head { display: flex; align-items: center; gap: 10px; width: 100%; padding: 12px; background: none; border: 0; cursor: pointer; text-align: left; font: inherit; }
.side-mod-head:hover { background: #fffaf3; }
.mod-no { flex: none; width: 32px; height: 32px; border-radius: 10px; display: grid; place-items: center; font-family: var(--font-mono); font-weight: 800; font-size: 15px; color: var(--brand-primary-dark); background: var(--surface-cream); border: 1px solid #fed7aa; }
.side-mod.open .mod-no { background: linear-gradient(135deg, var(--brand-primary), #fb923c); color: #fff; border-color: transparent; }
.mod-tt { display: flex; flex-direction: column; gap: 2px; min-width: 0; }
.mod-tt b { font-size: 15.5px; font-weight: 800; color: var(--brand-dark); line-height: 1.25; white-space: nowrap; overflow: hidden; text-overflow: ellipsis; }
.mod-tt small { font-size: 10.5px; color: var(--ink-soft); font-family: var(--font-mono); white-space: nowrap; overflow: hidden; text-overflow: ellipsis; }
.mod-meta { margin-left: auto; display: flex; align-items: center; gap: 7px; flex: none; }
.mod-progress { font-family: var(--font-mono); font-size: 10.5px; color: var(--ink-soft); background: #f3f4f6; border-radius: 999px; padding: 2px 8px; }
.side-mod.open .mod-progress { background: #ffedd5; color: var(--brand-primary-dark); }
.chev { font-size: 11px; color: var(--ink-soft); transition: transform .25s; }
.side-mod.open .chev { transform: rotate(180deg); color: var(--brand-primary-dark); }
.mod-bar { height: 3px; margin: 0 12px; background: #f3f4f6; border-radius: 999px; overflow: hidden; }
.mod-bar i { display: block; height: 100%; background: linear-gradient(90deg, var(--brand-primary), #fb923c); border-radius: 999px; transition: width .3s; }
/* 条目列表（随模块折叠） */
.mod-items { display: none; padding: 6px 8px 10px; border-top: 1px dashed #f5e7d3; }
.side-mod.open .mod-items { display: block; }
.side-item { display: flex; align-items: center; gap: 8px; padding: 7px 9px; border-radius: 9px; font-size: 13px; font-weight: 600; color: #4b5563; }
.side-item:hover { background: var(--surface-cream); color: var(--brand-dark); }
.side-item .ico { flex: none; font-size: 11px; opacity: .85; }
.side-item .ti { white-space: nowrap; overflow: hidden; text-overflow: ellipsis; }
.side-item .t { font-family: var(--font-mono); font-size: 10px; opacity: .6; margin-left: auto; flex: none; }
.side-item.current { background: var(--brand-dark); color: #fff; }
.side-item.current .ico { opacity: 1; }
.lesson-main { min-width: 0; }
.lesson-topbar { display: flex; align-items: center; gap: 12px; flex-wrap: wrap; margin-bottom: 18px; }
.lang-switch { display: inline-flex; background: #fff; border: 1px solid var(--border); border-radius: 999px; padding: 4px; gap: 2px; }
.lang-switch button { border: none; background: transparent; padding: 7px 16px; border-radius: 999px; font-size: 13px; font-weight: 700; color: #6b7280; cursor: pointer; font-family: inherit; transition: all .15s; }
.lang-switch button.on { background: var(--brand-dark); color: #fff; }
.mark-done { margin-left: auto; }
.lesson-article {
  background: #fff; border: 1px solid var(--border); border-radius: var(--radius);
  padding: clamp(22px, 4vw, 44px); box-shadow: var(--shadow-soft);
}
.lesson-article h1.lt { font-size: clamp(23px, 3vw, 31px); font-weight: 800; color: var(--brand-dark); line-height: 1.3; margin-bottom: 6px; }
.lesson-article .lt-en { color: var(--ink-soft); font-weight: 600; font-size: 15px; margin-bottom: 22px; }
.bilingual { display: grid; gap: 0; }
.bilingual .col { padding: 4px 0 26px; }
.bilingual.split { grid-template-columns: 1fr 1fr; gap: 36px; }
.bilingual.split .col + .col { border-left: 1px solid var(--border); padding-left: 36px; }
.bilingual .col .lang-tag { font-family: var(--font-mono); font-size: 11px; font-weight: 700; letter-spacing: .14em; color: var(--brand-secondary); margin-bottom: 14px; }
.md h2 { font-size: 20px; font-weight: 800; color: var(--brand-dark); margin: 26px 0 10px; }
.md h3 { font-size: 16.5px; font-weight: 800; color: var(--brand-dark); margin: 20px 0 8px; }
.md p { margin: 10px 0; font-size: 15px; }
.md ul, .md ol { margin: 10px 0 10px 22px; }
.md li { margin: 6px 0; font-size: 14.8px; }
.md blockquote { border-left: 3px solid var(--brand-primary); background: var(--surface-cream); border-radius: 0 12px 12px 0; padding: 12px 18px; margin: 14px 0; color: #57534e; }
.md blockquote p { margin: 4px 0; }
.md table { width: 100%; border-collapse: collapse; margin: 16px 0; font-size: 13.8px; background: #fff; border-radius: 10px; overflow: hidden; }
.md th { background: var(--brand-dark); color: #fff; text-align: left; padding: 9px 13px; font-size: 12.8px; }
.md td { border-bottom: 1px solid #eef0f3; padding: 9px 13px; vertical-align: top; }
.md tr:last-child td { border-bottom: none; }
.md code { font-family: var(--font-mono); background: #f4f4f5; border-radius: 6px; padding: 1.5px 7px; font-size: .92em; }
.md strong { color: var(--brand-dark); }
.lesson-nav { display: flex; justify-content: space-between; gap: 14px; margin-top: 26px; }
.lesson-nav a {
  flex: 1; background: #fff; border: 1px solid var(--border); border-radius: var(--radius-sm);
  padding: 14px 18px; font-weight: 700; font-size: 13.5px; color: #374151; transition: all .18s;
}
.lesson-nav a:hover { border-color: var(--brand-primary); color: var(--brand-primary-dark); }
.lesson-nav a span { display: block; font-size: 11px; color: #9ca3af; font-weight: 700; letter-spacing: .08em; margin-bottom: 3px; }
.lesson-nav a.next { text-align: right; }

/* ---------- 测验 ---------- */
.quiz-panel { margin-top: 26px; background: linear-gradient(180deg, var(--surface-cyan), #fff 140px); border: 1px solid #a5f3fc; border-radius: var(--radius); padding: clamp(20px, 3vw, 34px); }
.quiz-panel h2 { font-size: 20px; font-weight: 800; color: var(--brand-dark); display: flex; align-items: center; gap: 10px; }
.quiz-panel .qsub { color: #4b5563; font-size: 13.5px; margin: 6px 0 22px; }
.q-item { background: #fff; border: 1px solid var(--border); border-radius: var(--radius-sm); padding: 18px 20px; margin-bottom: 14px; }
.q-item .q-title { font-weight: 700; font-size: 15px; color: var(--brand-dark); margin-bottom: 4px; }
.q-item .q-title-en { font-size: 12.5px; color: #9ca3af; margin-bottom: 12px; font-weight: 600; }
.q-opt { display: flex; gap: 10px; align-items: flex-start; padding: 10px 14px; border: 1.5px solid var(--border); border-radius: 10px; margin: 8px 0; cursor: pointer; font-size: 14px; transition: all .15s; background: #fff; }
.q-opt:hover { border-color: #fdba74; background: #fff7ed; }
.q-opt .key { font-family: var(--font-mono); font-weight: 700; font-size: 12px; color: var(--ink-soft); background: #f4f4f5; border-radius: 6px; padding: 2px 7px; flex: none; margin-top: 1px; }
.q-opt small { display: block; color: #9ca3af; font-size: 11.5px; margin-top: 1px; }
.q-opt.correct { border-color: var(--brand-secondary); background: #f0fdfa; }
.q-opt.correct .key { background: var(--brand-secondary); color: #fff; }
.q-opt.wrong { border-color: #f87171; background: #fef2f2; }
.q-opt.reveal { border-color: #fbbf24; background: #fffbeb; }
.q-explain { margin-top: 12px; border-radius: 10px; background: #f8fafc; border: 1px dashed #cbd5e1; padding: 12px 16px; font-size: 13.5px; color: #475569; display: none; }
.q-explain.show { display: block; }
.q-explain b { color: var(--brand-dark); }
.quiz-result { margin-top: 18px; background: var(--brand-dark); color: #fff; border-radius: var(--radius-sm); padding: 18px 22px; font-weight: 700; display: none; }
.quiz-result.show { display: block; }
.quiz-result .score { font-size: 26px; font-weight: 800; color: var(--brand-amber); }

/* ---------- 视频位 ---------- */
.video-wrap { position: relative; border-radius: 14px; overflow: hidden; background: #0b1020; box-shadow: var(--shadow-soft); margin-bottom: 8px; }
.video-wrap video { width: 100%; aspect-ratio: 16/9; display: block; }
.video-subs {
  position: absolute; left: 5%; right: 5%; bottom: 8%;
  text-align: center; pointer-events: none; z-index: 2;
}
.video-subs .sub-zh {
  display: inline-block; font-size: clamp(14px, 2.3vw, 21px); font-weight: 700; color: #fff;
  line-height: 1.45; padding: 2px 12px;
  text-shadow: 0 1px 4px rgba(0, 0, 0, .95), 0 0 2px rgba(0, 0, 0, .9);
}
.video-subs .sub-en {
  display: inline-block; font-size: clamp(11px, 1.7vw, 14.5px); font-weight: 600; color: rgba(255, 255, 255, .92);
  line-height: 1.4; margin-top: 2px; padding: 0 10px;
  text-shadow: 0 1px 3px rgba(0, 0, 0, .95);
}
.sub-toggle {
  position: absolute; top: 12px; right: 12px; z-index: 3;
  border: none; background: rgba(17, 24, 39, .62); color: #fff;
  font-family: inherit; font-size: 12px; font-weight: 700;
  padding: 6px 13px; border-radius: 999px; cursor: pointer;
  backdrop-filter: blur(6px); transition: background .15s;
}
.sub-toggle:hover { background: rgba(17, 24, 39, .85); }
.video-note { font-size: 12.5px; color: var(--ink-soft); margin: 8px 2px 22px; }
.video-slot {
  display: flex; gap: 18px; align-items: flex-start;
  border: 1.5px dashed #fed7aa; background: linear-gradient(180deg, #fffbeb, #fff7ed);
  border-radius: 14px; padding: 20px 22px; margin-bottom: 24px;
}
.video-slot-ico { font-size: 30px; line-height: 1; padding-top: 2px; }
.video-slot-body b { color: var(--brand-dark); font-size: 15px; }
.video-slot-body p { font-size: 13.5px; color: #57534e; margin: 8px 0; }
.video-slot-actions { display: flex; gap: 10px; flex-wrap: wrap; }
.video-slot-tip { font-size: 12.5px !important; color: #78716c !important; border-top: 1px dashed #e7d8c4; padding-top: 10px; }
.video-slot-tip code { background: #fff; border: 1px solid #f3e3ce; border-radius: 5px; padding: 1px 6px; font-family: var(--font-mono); font-size: 11.5px; }

/* ---------- 响应式 ---------- */
@media (max-width: 960px) {
  .hero { grid-template-columns: 1fr; padding-top: 56px; }
  .feature-grid, .tool-grid { grid-template-columns: repeat(2, 1fr); }
  .module-grid { grid-template-columns: repeat(2, 1fr); }
  .lesson-layout { grid-template-columns: 1fr; }
  .lesson-side { position: static; max-height: none; }
  .bilingual.split { grid-template-columns: 1fr; }
  .bilingual.split .col + .col { border-left: none; padding-left: 0; border-top: 1px solid var(--border); padding-top: 24px; }
  .course-title small { display: none; }
}
@media (max-width: 620px) {
  .feature-grid, .tool-grid, .module-grid { grid-template-columns: 1fr; }
  .nav-links a:not(.keep) { display: none; }
  .tool-band { padding: 30px 22px; }
  .container { width: calc(100% - 36px); }
  .course-title b { max-width: 150px; }
}

/* ---------- 英文旁白音频 / PDF 讲义 / 英文原文 ---------- */
.audio-wrap { border: 1px solid var(--border); border-radius: 14px; background: var(--surface-cream, #fffaf3); padding: 16px 18px; margin-bottom: 12px; box-shadow: var(--shadow-soft); }
.audio-wrap .audio-label { font-weight: 700; font-size: 14px; color: var(--brand-dark); margin-bottom: 10px; }
.audio-wrap audio { width: 100%; display: block; }
.pdf-row { margin: 10px 2px 18px; }
.orig-panel { background: #fff; border: 1px dashed var(--border); border-radius: var(--radius-sm, 12px); padding: 14px 20px; margin: 22px 0; }
.orig-panel summary { cursor: pointer; font-weight: 700; color: var(--brand-dark); font-size: 14.5px; list-style: none; display: flex; align-items: center; gap: 8px; }
.orig-panel summary::marker { content: none; }
.orig-panel summary::after { content: "展开 ▾"; font-size: 12.5px; color: var(--brand-primary); font-weight: 600; margin-left: auto; }
.orig-panel[open] summary::after { content: "收起 ▴"; }
.orig-panel .orig-body { margin-top: 14px; border-top: 1px solid var(--border); padding-top: 12px; font-size: 14px; color: #44403c; }

/* ---------- 原文内嵌配图 ---------- */
.md-fig { margin: 16px 0; }
.md-fig img { display: block; width: 100%; max-width: 720px; margin: 0 auto; border: 1px solid var(--border); border-radius: 12px; box-shadow: var(--shadow-soft); background: #fff; }
.md-fig figcaption { text-align: center; font-size: 12px; color: var(--ink-soft); margin-top: 8px; }

/* ---------- 本土化贴士 ---------- */
.cn-tips { background: linear-gradient(180deg, #f0fdf9, #fff 55%); border: 1px solid #99f6e4; border-left: 4px solid var(--brand-secondary, #0f766e); border-radius: 14px; padding: 16px 20px 10px; margin: 14px 0 20px; }
.cn-tips-head { font-weight: 800; font-size: 14.5px; color: #0f766e; margin-bottom: 10px; }
.cn-tips-body { font-size: 14px; color: #334155; }
.cn-tips-body p { margin: 8px 0; }
.cn-tips-body table { width: 100%; border-collapse: collapse; margin: 10px 0; font-size: 13.5px; }
.cn-tips-body th { background: #0f766e; color: #fff; }
.cn-tips-body th, .cn-tips-body td { border: 1px solid #ccfbf1; padding: 7px 10px; text-align: left; }
.cn-tips-body tr:nth-child(even) td { background: #f0fdfa; }
.cn-tips-body .md-fig { max-width: 640px; margin: 12px auto; }
.cn-tips-body code { background: #ccfbf1; color: #0f766e; padding: 2px 8px; border-radius: 8px; display: block; margin: 8px 0; line-height: 1.7; }

/* ---------- B 站内嵌播放器 ---------- */
.bili-wrap { aspect-ratio: 16/9; background: #000; }
.bili-wrap iframe { width: 100%; height: 100%; display: block; border: 0; }

/* ---------- Hero 官方信任条 ---------- */
.trust-row { display: flex; flex-wrap: wrap; gap: 10px; margin-top: 18px; }
.trust-row span { display: inline-flex; align-items: center; gap: 6px; background: #fff; border: 1px solid var(--border); border-radius: 999px; padding: 7px 14px; font-size: 12.5px; font-weight: 700; color: #57534e; box-shadow: var(--shadow-soft); }