/* ============================================================
   俄语学习社区 · 样式表
   设计目标：现代、简约、清爽，主色深蓝 + 暖红点缀
   ============================================================ */

:root {
  --bg: #f6f5f2;
  --surface: #ffffff;
  --surface-2: #fbfaf8;
  --ink: #1d2433;
  --ink-soft: #3c4555;
  --muted: #747d8c;
  --line: #e7e3dc;
  --primary: #1f3a5f;
  --primary-soft: #e8eef5;
  --accent: #e4572e;
  --accent-soft: #fdeee9;
  --teal: #2a9d8f;
  --gold: #e0a83b;
  --radius: 16px;
  --radius-sm: 10px;
  --shadow: 0 6px 24px rgba(31, 58, 95, 0.08);
  --shadow-lg: 0 18px 50px rgba(31, 58, 95, 0.16);
  --maxw: 1120px;
  --font-cn: "Noto Sans SC", "PingFang SC", "Microsoft YaHei", system-ui, sans-serif;
  --font-ru: "PT Serif", "Noto Serif SC", Georgia, serif;
  --font-script: "Marck Script", cursive;
}

html[data-theme="dark"] {
  --bg: #11161f;
  --surface: #1a2130;
  --surface-2: #161c28;
  --ink: #e9eef6;
  --ink-soft: #c4cdda;
  --muted: #8b97a8;
  --line: #2a3242;
  --primary: #7fb0ef;
  --primary-soft: #1d2940;
  --accent: #ff7a59;
  --accent-soft: #3a2218;
  --teal: #4fc4b5;
  --gold: #f0c065;
  --shadow: 0 6px 24px rgba(0, 0, 0, 0.35);
  --shadow-lg: 0 18px 50px rgba(0, 0, 0, 0.5);
}

* { box-sizing: border-box; }

html { scroll-behavior: smooth; scroll-padding-top: 84px; }

body {
  margin: 0;
  font-family: var(--font-cn);
  background: var(--bg);
  color: var(--ink);
  line-height: 1.7;
  -webkit-font-smoothing: antialiased;
  transition: background .35s ease, color .35s ease;
}

.container { width: 100%; max-width: var(--maxw); margin: 0 auto; padding: 0 24px; }

a { color: inherit; text-decoration: none; }

/* ---------- Header ---------- */
.site-header {
  position: sticky; top: 0; z-index: 50;
  background: color-mix(in srgb, var(--surface) 86%, transparent);
  backdrop-filter: saturate(160%) blur(12px);
  border-bottom: 1px solid var(--line);
}
.nav-wrap { display: flex; align-items: center; justify-content: space-between; height: 68px; }
.brand { display: flex; align-items: baseline; gap: 10px; }
.brand-ru {
  font-family: var(--font-ru); font-weight: 700; font-size: 22px;
  color: var(--primary); letter-spacing: 1px;
}
.brand-cn { font-weight: 500; font-size: 15px; color: var(--ink); }
.nav { display: flex; gap: 26px; }
.nav a {
  font-size: 14.5px; color: var(--ink-soft); position: relative; padding: 6px 0;
  transition: color .2s;
}
.nav a::after {
  content: ""; position: absolute; left: 0; bottom: 0; height: 2px; width: 0;
  background: var(--accent); transition: width .25s ease;
}
.nav a:hover { color: var(--primary); }
.nav a:hover::after { width: 100%; }
.nav-tools { display: flex; align-items: center; gap: 10px; }
.theme-toggle {
  width: 40px; height: 40px; border-radius: 50%; border: 1px solid var(--line);
  background: var(--surface); cursor: pointer; font-size: 18px; line-height: 1;
  transition: transform .25s, background .25s;
}
.theme-toggle:hover { transform: rotate(-18deg) scale(1.05); background: var(--primary-soft); }
.nav-burger { display: none; background: none; border: none; font-size: 24px; color: var(--ink); cursor: pointer; }

/* ---------- Hero ---------- */
.hero { position: relative; overflow: hidden; padding: 70px 0 90px; }
.hero::before {
  content: ""; position: absolute; inset: 0;
  background:
    radial-gradient(60% 90% at 85% 10%, var(--primary-soft) 0%, transparent 60%),
    radial-gradient(50% 70% at 5% 95%, var(--accent-soft) 0%, transparent 55%);
  z-index: 0;
}
.hero-inner { position: relative; z-index: 1; display: grid; grid-template-columns: 1.15fr .85fr; gap: 48px; align-items: center; }
.eyebrow { font-family: var(--font-ru); color: var(--accent); letter-spacing: 3px; font-size: 13px; font-weight: 700; margin: 0 0 14px; }
.hero h1 { font-size: clamp(30px, 4.5vw, 50px); line-height: 1.18; margin: 0 0 18px; font-weight: 700; letter-spacing: -.5px; }
.lead { font-size: 16px; color: var(--ink-soft); max-width: 540px; margin: 0 0 28px; }
.hero-cta { display: flex; gap: 14px; flex-wrap: wrap; }
.btn {
  display: inline-flex; align-items: center; gap: 8px; padding: 12px 22px;
  border-radius: 999px; font-size: 15px; font-weight: 500; cursor: pointer;
  border: 1px solid transparent; transition: transform .2s, box-shadow .2s, background .2s;
}
.btn-primary { background: var(--accent); color: #fff; box-shadow: 0 8px 20px rgba(228, 87, 46, .3); }
.btn-primary:hover { transform: translateY(-2px); box-shadow: 0 14px 30px rgba(228, 87, 46, .4); }
.btn-ghost { background: transparent; border-color: var(--line); color: var(--ink); }
.btn-ghost:hover { background: var(--surface); transform: translateY(-2px); }
.hero-stats { display: flex; gap: 30px; margin-top: 38px; flex-wrap: wrap; }
.hero-stats div { display: flex; flex-direction: column; }
.hero-stats strong { font-size: 26px; color: var(--primary); font-family: var(--font-ru); }
.hero-stats span { font-size: 12.5px; color: var(--muted); }

.hero-card {
  background: var(--surface); border: 1px solid var(--line); border-radius: var(--radius);
  padding: 30px; box-shadow: var(--shadow-lg); position: relative;
}
.speech-bubble { border-left: 4px solid var(--accent); padding-left: 18px; }
.ru-big { font-family: var(--font-ru); font-size: 40px; margin: 0 0 6px; color: var(--primary); }
.ru-sub { font-family: var(--font-ru); color: var(--muted); margin: 0 0 16px; font-size: 16px; }
.cn-sub { color: var(--ink-soft); margin: 0; font-size: 15px; }
.hero-card-foot { display: flex; align-items: center; gap: 10px; margin-top: 24px; padding-top: 16px; border-top: 1px dashed var(--line); color: var(--muted); font-size: 13px; }
.hero-card-foot .dot { width: 5px; height: 5px; border-radius: 50%; background: var(--accent); }

/* ---------- Section ---------- */
.section { padding: 84px 0; }
.section-alt { background: var(--surface-2); border-top: 1px solid var(--line); border-bottom: 1px solid var(--line); }
.section-head { max-width: 720px; margin: 0 auto 46px; text-align: center; }
.kicker { font-family: var(--font-ru); color: var(--accent); letter-spacing: 2px; font-size: 12.5px; font-weight: 700; margin: 0 0 10px; }
.section-head h2 { font-size: clamp(24px, 3.4vw, 34px); margin: 0 0 12px; font-weight: 700; letter-spacing: -.3px; }
.section-intro { color: var(--ink-soft); font-size: 15.5px; margin: 0; }

/* ---------- Cards ---------- */
.card {
  background: var(--surface); border: 1px solid var(--line); border-radius: var(--radius);
  padding: 26px; box-shadow: var(--shadow); transition: transform .25s, box-shadow .25s;
}
.card:hover { transform: translateY(-4px); box-shadow: var(--shadow-lg); }
.card h3 { margin: 0 0 12px; font-size: 18px; color: var(--primary); }
.card p { margin: 0 0 12px; color: var(--ink-soft); font-size: 15px; }
.card p:last-child { margin-bottom: 0; }
.card strong { color: var(--ink); }
.tick, .steps { margin: 0 0 12px; padding-left: 20px; color: var(--ink-soft); font-size: 15px; }
.tick li, .steps li { margin-bottom: 6px; }
.steps { list-style: decimal; }

/* ---------- About grid ---------- */
.about-grid { display: grid; grid-template-columns: repeat(2, 1fr); gap: 22px; }
.factbar { display: flex; flex-wrap: wrap; gap: 16px; margin-top: 30px; justify-content: center; }
.fact { display: flex; flex-direction: column; align-items: center; background: var(--primary-soft); border-radius: var(--radius-sm); padding: 14px 22px; }
.fact-ru { font-family: var(--font-ru); font-size: 19px; color: var(--primary); }
.fact-cn { font-size: 12.5px; color: var(--muted); margin-top: 2px; }

/* ---------- Alphabet ---------- */
.alpha-toolbar { text-align: center; margin-bottom: 18px; }
.hint { font-size: 13.5px; color: var(--muted); background: var(--surface); border: 1px dashed var(--line); padding: 8px 16px; border-radius: 999px; }
.alpha-grid { display: grid; grid-template-columns: repeat(auto-fill, minmax(118px, 1fr)); gap: 14px; }
.alpha-card {
  background: var(--surface); border: 1px solid var(--line); border-radius: var(--radius-sm);
  padding: 16px 12px; text-align: center; cursor: pointer; position: relative; overflow: hidden;
  transition: transform .2s, box-shadow .2s, border-color .2s; min-height: 118px;
  display: flex; flex-direction: column; justify-content: center;
}
.alpha-card:hover { transform: translateY(-4px); box-shadow: var(--shadow); border-color: var(--accent); }
.alpha-card .big { font-family: var(--font-ru); font-size: 34px; line-height: 1; color: var(--primary); }
.alpha-card .name { font-size: 12px; color: var(--muted); margin-top: 6px; }
.alpha-card .sound { font-size: 11.5px; color: var(--ink-soft); margin-top: 3px; font-family: var(--font-ru); }
.alpha-card .ex { font-size: 11px; color: var(--accent); margin-top: 4px; opacity: 0; max-height: 0; transition: opacity .25s, max-height .25s; }
.alpha-card.open .ex { opacity: 1; max-height: 30px; }
.alpha-card .type-tag { position: absolute; top: 8px; right: 8px; font-size: 9px; padding: 2px 6px; border-radius: 999px; background: var(--primary-soft); color: var(--primary); }
.alpha-note { font-size: 13px; color: var(--muted); margin-top: 22px; text-align: center; }

/* ---------- Pronunciation ---------- */
.pron-grid { display: grid; grid-template-columns: repeat(3, 1fr); gap: 20px; }

/* ---------- Tabs ---------- */
.tabs { background: var(--surface); border: 1px solid var(--line); border-radius: var(--radius); overflow: hidden; box-shadow: var(--shadow); }
.tab-bar { display: flex; flex-wrap: wrap; border-bottom: 1px solid var(--line); background: var(--surface-2); }
.tab-btn { flex: 1 1 auto; padding: 14px 12px; background: none; border: none; cursor: pointer; font-family: var(--font-cn); font-size: 14.5px; color: var(--muted); border-bottom: 3px solid transparent; transition: color .2s, border-color .2s, background .2s; }
.tab-btn:hover { color: var(--primary); }
.tab-btn.active { color: var(--primary); border-bottom-color: var(--accent); font-weight: 500; background: var(--surface); }
.tab-panel { display: none; padding: 28px; animation: fade .3s ease; }
.tab-panel.active { display: block; }
.tab-panel p { color: var(--ink-soft); margin: 0 0 14px; }
.tab-panel .note { background: var(--accent-soft); border-radius: var(--radius-sm); padding: 12px 16px; font-size: 14px; }
.tab-panel .example { background: var(--primary-soft); border-radius: var(--radius-sm); padding: 12px 16px; font-size: 14px; }
@keyframes fade { from { opacity: 0; transform: translateY(6px); } to { opacity: 1; transform: none; } }

/* ---------- Data table ---------- */
.data-table { width: 100%; border-collapse: collapse; margin: 6px 0 14px; font-size: 14.5px; }
.data-table th, .data-table td { text-align: left; padding: 11px 14px; border-bottom: 1px solid var(--line); }
.data-table th { background: var(--surface-2); color: var(--primary); font-weight: 600; }
.data-table td { color: var(--ink-soft); }
.data-table .ru { font-family: var(--font-ru); color: var(--ink); }
.data-table tr:hover td { background: var(--surface-2); }

/* ---------- Dialogue ---------- */
.dialogue-picker { display: flex; flex-wrap: wrap; gap: 10px; justify-content: center; margin-bottom: 28px; }
.dlg-chip { padding: 9px 18px; border-radius: 999px; border: 1px solid var(--line); background: var(--surface); cursor: pointer; font-size: 14px; color: var(--ink-soft); transition: all .2s; }
.dlg-chip:hover { border-color: var(--accent); color: var(--primary); }
.dlg-chip.active { background: var(--accent); color: #fff; border-color: var(--accent); }
.dialogue-stage { max-width: 760px; margin: 0 auto; background: var(--surface); border: 1px solid var(--line); border-radius: var(--radius); padding: 30px; box-shadow: var(--shadow); }
.dlg-meta { display: flex; align-items: center; gap: 12px; margin-bottom: 20px; flex-wrap: wrap; }
.dlg-title { font-size: 20px; font-weight: 700; color: var(--primary); }
.dlg-toggle { margin-left: auto; display: flex; border: 1px solid var(--line); border-radius: 999px; overflow: hidden; }
.dlg-toggle button { border: none; background: var(--surface); padding: 7px 14px; cursor: pointer; font-size: 13px; color: var(--muted); font-family: var(--font-cn); }
.dlg-toggle button.active { background: var(--primary); color: #fff; }
.dlg-line { display: flex; gap: 14px; padding: 14px 0; border-bottom: 1px dashed var(--line); align-items: flex-start; }
.dlg-line:last-child { border-bottom: none; }
.dlg-role { flex: 0 0 64px; font-size: 13px; font-weight: 600; color: var(--accent); padding-top: 3px; }
.dlg-text { flex: 1; }
.dlg-ru { font-family: var(--font-ru); font-size: 17px; color: var(--ink); }
.dlg-tr { font-size: 13px; color: var(--muted); margin-top: 2px; font-style: italic; }
.dlg-cn { font-size: 14.5px; color: var(--ink-soft); margin-top: 2px; }
.dlg-vocab { margin-top: 18px; padding-top: 16px; border-top: 1px solid var(--line); }
.dlg-vocab h4 { margin: 0 0 10px; font-size: 14px; color: var(--primary); }
.dlg-vocab ul { margin: 0; padding-left: 18px; font-size: 14px; color: var(--ink-soft); }
.dlg-vocab li { margin-bottom: 5px; }
.dlg-vocab .ru { font-family: var(--font-ru); color: var(--ink); }

/* ---------- Practice ---------- */
.practice-grid { display: grid; grid-template-columns: repeat(auto-fill, minmax(260px, 1fr)); gap: 20px; }
.practice-card { background: var(--surface); border: 1px solid var(--line); border-radius: var(--radius); padding: 24px; box-shadow: var(--shadow); transition: transform .25s, box-shadow .25s; }
.practice-card:hover { transform: translateY(-4px); box-shadow: var(--shadow-lg); }
.practice-card h3 { margin: 0 0 4px; font-size: 17px; color: var(--primary); display: flex; align-items: center; gap: 8px; }
.practice-card .emoji { font-size: 20px; }
.practice-card .p-sub { font-size: 12.5px; color: var(--muted); margin: 0 0 16px; }
.p-item { display: flex; justify-content: space-between; gap: 10px; padding: 9px 0; border-bottom: 1px dashed var(--line); font-size: 14.5px; }
.p-item:last-child { border-bottom: none; }
.p-item .ru { font-family: var(--font-ru); color: var(--ink); }
.p-item .cn { color: var(--muted); }

/* ---------- Quiz ---------- */
.quiz-wrap { max-width: 820px; margin: 0 auto; display: flex; flex-direction: column; gap: 18px; }
.q-card { background: var(--surface); border: 1px solid var(--line); border-radius: var(--radius); padding: 22px 24px; box-shadow: var(--shadow); }
.q-num { font-size: 13px; color: var(--accent); font-weight: 700; margin-bottom: 6px; }
.q-text { font-size: 16px; margin: 0 0 14px; color: var(--ink); }
.q-text .ru { font-family: var(--font-ru); }
.q-options { display: grid; gap: 10px; }
.q-opt { display: flex; align-items: center; gap: 12px; padding: 11px 14px; border: 1px solid var(--line); border-radius: var(--radius-sm); cursor: pointer; font-size: 14.5px; color: var(--ink-soft); transition: all .18s; }
.q-opt:hover { border-color: var(--primary); background: var(--surface-2); }
.q-opt input { accent-color: var(--accent); width: 16px; height: 16px; }
.q-opt.correct { background: #e6f5ec; border-color: var(--teal); color: #1c6b48; }
.q-opt.wrong { background: #fdeaea; border-color: #e07a7a; color: #a33131; }
.q-explain { margin-top: 12px; font-size: 13.5px; color: var(--muted); display: none; }
.q-card.revealed .q-explain { display: block; }
.quiz-actions { display: flex; gap: 14px; justify-content: center; margin-top: 26px; }
.quiz-result { max-width: 820px; margin: 26px auto 0; text-align: center; background: var(--primary-soft); border-radius: var(--radius); padding: 28px; }
.quiz-result h3 { margin: 0 0 8px; font-size: 24px; color: var(--primary); }
.quiz-result p { margin: 0; color: var(--ink-soft); }

/* ---------- Footer ---------- */
.site-footer { background: var(--surface); border-top: 1px solid var(--line); padding: 50px 0 0; }
.footer-inner { display: flex; justify-content: space-between; gap: 40px; flex-wrap: wrap; padding-bottom: 36px; }
.footer-brand { max-width: 420px; }
.footer-brand p { color: var(--muted); font-size: 14px; margin-top: 12px; }
.footer-links { display: flex; flex-direction: column; gap: 10px; }
.footer-links a { color: var(--ink-soft); font-size: 14.5px; transition: color .2s; }
.footer-links a:hover { color: var(--accent); }
.footer-base { border-top: 1px solid var(--line); text-align: center; padding: 18px; font-size: 12.5px; color: var(--muted); }

/* ---------- To top ---------- */
.to-top { position: fixed; right: 24px; bottom: 24px; width: 46px; height: 46px; border-radius: 50%; background: var(--accent); color: #fff; border: none; font-size: 20px; cursor: pointer; box-shadow: var(--shadow-lg); opacity: 0; pointer-events: none; transition: opacity .3s, transform .3s; z-index: 40; }
.to-top.show { opacity: 1; pointer-events: auto; }
.to-top:hover { transform: translateY(-3px); }

/* ---------- Responsive ---------- */
@media (max-width: 880px) {
  .hero-inner { grid-template-columns: 1fr; }
  .hero-card { order: -1; }
  .about-grid { grid-template-columns: 1fr; }
  .pron-grid { grid-template-columns: 1fr; }
  .nav { position: fixed; top: 68px; left: 0; right: 0; background: var(--surface); flex-direction: column; gap: 0; padding: 8px 0; border-bottom: 1px solid var(--line); transform: translateY(-130%); transition: transform .3s; box-shadow: var(--shadow); }
  .nav.open { transform: none; }
  .nav a { padding: 14px 24px; }
  .nav-burger { display: block; }
}
@media (max-width: 520px) {
  .hero-stats { gap: 18px; }
  .section { padding: 60px 0; }
  .alpha-grid { grid-template-columns: repeat(auto-fill, minmax(96px, 1fr)); }
}