/* ============================================================
   AI 背单词 — 即将推出式介绍页
   纯静态样式：无外部字体、无图片，排版与配色撑住页面。
   语言机制：html[lang] 切换，data-lang 元素按语言显示/隐藏。
   ============================================================ */

/* ---------- 语言可见性（核心机制） ---------- */
html[lang="en"] [data-lang="zh"] { display: none; }
html[lang="zh-CN"] [data-lang="en"],
html[lang="zh"] [data-lang="en"] { display: none; }

/* 语言切换按钮的激活态（跟随 html[lang]，无需 JS 同步样式） */
.lang-opt-zh, .lang-opt-en { opacity: 0.62; }
html[lang="zh-CN"] .lang-opt-zh,
html[lang="zh"] .lang-opt-zh { opacity: 1; background: var(--ink); color: var(--paper); }
html[lang="en"] .lang-opt-en { opacity: 1; background: var(--ink); color: var(--paper); }

/* ---------- 设计变量 ---------- */
:root {
  --paper: #f5efe3;
  --paper-deep: #ece3d0;
  --card: #fffdf6;
  --ink: #2a2620;
  --ink-soft: #6b6353;
  --ink-faint: #998f7c;
  --line: #d9cdb4;
  --line-soft: #e7ddc8;
  --accent: #b93a22;
  --accent-deep: #932c18;
  --accent-soft: #f4ddd5;
  --ok: #4a7c59;

  --font-serif: Georgia, "Times New Roman", "Songti SC", "STSong", "SimSun",
    "Noto Serif CJK SC", "Source Han Serif SC", serif;
  --font-sans: -apple-system, BlinkMacSystemFont, "Segoe UI", "PingFang SC",
    "Hiragino Sans GB", "Microsoft YaHei", "Noto Sans SC", Arial, sans-serif;
  --font-mono: "Cascadia Mono", "SF Mono", Consolas, "Liberation Mono", Menlo,
    monospace;

  --radius: 14px;
  --shadow-card: 0 14px 34px rgba(42, 38, 32, 0.09);
  --shadow-soft: 0 6px 18px rgba(42, 38, 32, 0.07);
  --header-h: 64px;
}

/* ---------- 基础 ---------- */
*, *::before, *::after { box-sizing: border-box; }

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

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

img, svg { max-width: 100%; }

h1, h2, h3, h4 {
  font-family: var(--font-serif);
  line-height: 1.28;
  margin: 0 0 0.5em;
  font-weight: 700;
  letter-spacing: 0.01em;
}

p { margin: 0 0 1em; }
p:last-child { margin-bottom: 0; }

a { color: var(--accent-deep); text-decoration: none; }
a:hover { text-decoration: underline; }

:focus-visible {
  outline: 2px solid var(--accent);
  outline-offset: 2px;
  border-radius: 4px;
}

.container {
  width: min(1120px, calc(100% - 48px));
  margin: 0 auto;
}

.container-narrow { width: min(820px, calc(100% - 48px)); }

.skip-link {
  position: absolute;
  left: 16px;
  top: -48px;
  z-index: 100;
  padding: 10px 16px;
  background: var(--ink);
  color: var(--paper);
  border-radius: 0 0 10px 10px;
  font-size: 0.9rem;
  transition: top 0.2s ease;
}
.skip-link:focus { top: 0; text-decoration: none; }

/* ---------- 顶部导航 ---------- */
.site-header {
  position: sticky;
  top: 0;
  z-index: 50;
  background: rgba(245, 239, 227, 0.92);
  backdrop-filter: blur(10px);
  -webkit-backdrop-filter: blur(10px);
  border-bottom: 1px solid var(--line);
}

.header-inner {
  display: flex;
  align-items: center;
  gap: 28px;
  min-height: var(--header-h);
  flex-wrap: wrap;
  padding: 8px 0;
}

.brand {
  display: inline-flex;
  align-items: center;
  gap: 10px;
  color: var(--ink);
  font-family: var(--font-serif);
  font-weight: 700;
  font-size: 1.12rem;
  letter-spacing: 0.02em;
}
.brand:hover { text-decoration: none; }

.brand-mark {
  display: inline-flex;
  align-items: center;
  justify-content: center;
  width: 34px;
  height: 34px;
  border-radius: 9px;
  background: var(--accent);
  color: var(--card);
  font-family: var(--font-serif);
  font-size: 1.05rem;
  line-height: 1;
  box-shadow: var(--shadow-soft);
}

.site-nav {
  display: flex;
  gap: 4px;
  margin-left: auto;
  flex-wrap: wrap;
}

.site-nav a {
  color: var(--ink-soft);
  padding: 6px 12px;
  border-radius: 8px;
  font-size: 0.95rem;
  transition: color 0.15s ease, background 0.15s ease;
}
.site-nav a:hover {
  color: var(--ink);
  background: var(--paper-deep);
  text-decoration: none;
}

.lang-switch {
  display: inline-flex;
  border: 1px solid var(--line);
  border-radius: 10px;
  overflow: hidden;
  background: var(--card);
}

.lang-opt {
  appearance: none;
  border: 0;
  background: transparent;
  font-family: var(--font-sans);
  font-size: 0.88rem;
  padding: 6px 14px;
  cursor: pointer;
  color: var(--ink);
  transition: background 0.15s ease, color 0.15s ease, opacity 0.15s ease;
}

/* ---------- 按钮 ---------- */
.btn {
  display: inline-flex;
  align-items: center;
  justify-content: center;
  gap: 8px;
  padding: 12px 26px;
  border-radius: 12px;
  font-size: 1rem;
  font-weight: 600;
  border: 1px solid transparent;
  transition: transform 0.15s ease, box-shadow 0.15s ease,
    background 0.15s ease, border-color 0.15s ease;
}
.btn:hover { text-decoration: none; transform: translateY(-2px); }

.btn-solid {
  background: var(--accent);
  color: var(--card);
  box-shadow: 0 8px 20px rgba(185, 58, 34, 0.28);
}
.btn-solid:hover { background: var(--accent-deep); }

.btn-ghost {
  background: transparent;
  color: var(--ink);
  border-color: var(--line);
}
.btn-ghost:hover { border-color: var(--ink-soft); background: var(--card); }

/* ---------- Hero ---------- */
.hero {
  position: relative;
  padding: 84px 0 96px;
  background:
    radial-gradient(1100px 480px at 85% -12%, rgba(185, 58, 34, 0.07), transparent 62%),
    radial-gradient(760px 420px at -10% 108%, rgba(42, 38, 32, 0.05), transparent 60%),
    linear-gradient(180deg, #f8f3e9 0%, var(--paper) 100%);
  border-bottom: 1px solid var(--line);
  overflow: hidden;
}

.hero-grid {
  display: grid;
  grid-template-columns: minmax(0, 1.08fr) minmax(0, 0.92fr);
  gap: 56px;
  align-items: center;
}

.status-pill {
  display: inline-flex;
  align-items: center;
  gap: 9px;
  margin: 0 0 22px;
  padding: 6px 15px;
  border: 1px solid var(--line);
  border-radius: 999px;
  background: var(--card);
  font-family: var(--font-mono);
  font-size: 0.82rem;
  color: var(--ink-soft);
  letter-spacing: 0.03em;
}

.status-dot {
  width: 8px;
  height: 8px;
  border-radius: 50%;
  background: var(--accent);
  box-shadow: 0 0 0 0 rgba(185, 58, 34, 0.45);
  animation: pulse 2.4s ease-out infinite;
}

@keyframes pulse {
  0% { box-shadow: 0 0 0 0 rgba(185, 58, 34, 0.45); }
  70% { box-shadow: 0 0 0 9px rgba(185, 58, 34, 0); }
  100% { box-shadow: 0 0 0 0 rgba(185, 58, 34, 0); }
}

.hero-title {
  font-size: clamp(2rem, 4.6vw, 3.15rem);
  margin: 0 0 20px;
}

.hero-title em {
  font-style: normal;
  color: var(--accent-deep);
  border-bottom: 3px solid var(--accent-soft);
}

.hero-sub {
  font-size: 1.08rem;
  color: var(--ink-soft);
  max-width: 56ch;
  margin-bottom: 30px;
}

.hero-cta {
  display: flex;
  gap: 14px;
  flex-wrap: wrap;
  margin-bottom: 12px;
}

.hero-cta-note {
  margin: 0 0 22px;
  font-size: 0.88rem;
  letter-spacing: 0.01em;
}

.hero-cta-note a {
  color: inherit;
  font-weight: 700;
  text-decoration: underline;
  text-underline-offset: 3px;
}

.fact-chips {
  list-style: none;
  display: flex;
  flex-wrap: wrap;
  gap: 10px;
  margin: 0;
  padding: 0;
}

.fact-chips li {
  font-family: var(--font-mono);
  font-size: 0.8rem;
  letter-spacing: 0.02em;
  color: var(--ink-soft);
  background: var(--card);
  border: 1px dashed var(--line);
  border-radius: 8px;
  padding: 4px 12px;
}

/* ---------- Hero 卡片示意 ---------- */
.hero-visual { margin: 0; position: relative; }

.mock-note {
  font-family: var(--font-mono);
  font-size: 0.74rem;
  letter-spacing: 0.05em;
  color: var(--ink-faint);
  text-align: center;
  margin-bottom: 14px;
}

.mock-stack { position: relative; }

.stack-layer {
  position: absolute;
  inset: 0;
  border: 1px solid var(--line);
  border-radius: 18px;
  background: var(--card);
}

.stack-a {
  transform: rotate(-4.5deg) translate(-14px, 10px);
  opacity: 0.55;
}

.stack-b {
  transform: rotate(3.5deg) translate(12px, -8px);
  opacity: 0.75;
}

.mock-card {
  position: relative;
  z-index: 1;
  background: var(--card);
  border: 1px solid var(--line);
  border-radius: 18px;
  box-shadow: var(--shadow-card);
  padding: 26px 28px 24px;
}

.mock-queue {
  font-family: var(--font-mono);
  font-size: 0.8rem;
  color: var(--accent-deep);
  background: var(--accent-soft);
  border-radius: 999px;
  display: inline-block;
  padding: 3px 13px;
  margin: 0 0 16px;
}

.mock-word-row {
  display: flex;
  align-items: baseline;
  gap: 12px;
  margin-bottom: 14px;
}

.mock-word {
  font-family: var(--font-serif);
  font-style: italic;
  font-size: 2.55rem;
  line-height: 1.1;
  margin: 0;
}

.mock-pos {
  font-family: var(--font-mono);
  font-size: 0.86rem;
  color: var(--card);
  background: var(--ink);
  border-radius: 6px;
  padding: 2px 8px;
}

.mock-divider {
  height: 1px;
  background: var(--line-soft);
  margin-bottom: 14px;
}

.mock-gloss-label {
  font-family: var(--font-mono);
  font-size: 0.74rem;
  letter-spacing: 0.14em;
  color: var(--ink-faint);
  margin: 0 0 4px;
}

.mock-gloss-text {
  font-size: 1.02rem;
  color: var(--ink);
  margin-bottom: 20px;
}

.mock-btns {
  display: grid;
  grid-template-columns: repeat(3, 1fr);
  gap: 10px;
  margin-bottom: 18px;
}

.mock-btn {
  text-align: center;
  border: 1px solid var(--line);
  border-radius: 10px;
  padding: 9px 0;
  font-size: 0.95rem;
  color: var(--ink);
  background: var(--paper);
}

.mock-btn-again {
  color: var(--accent-deep);
  border-color: rgba(185, 58, 34, 0.4);
  background: var(--accent-soft);
}

.mock-progress-label {
  font-family: var(--font-mono);
  font-size: 0.8rem;
  color: var(--ink-soft);
  display: block;
  margin-bottom: 7px;
}

.mock-progress-bar {
  display: block;
  height: 7px;
  border-radius: 999px;
  background: var(--paper-deep);
  overflow: hidden;
}

.mock-progress-bar i {
  display: block;
  height: 100%;
  border-radius: 999px;
  background: linear-gradient(90deg, var(--accent), var(--accent-deep));
}

/* ---------- 通用 Section ---------- */
.section { padding: 88px 0; }
.section-alt { background: var(--paper-deep); border-top: 1px solid var(--line); border-bottom: 1px solid var(--line); }
section[id] { scroll-margin-top: calc(var(--header-h) + 16px); }

.section-head { margin-bottom: 44px; }

.eyebrow {
  display: flex;
  align-items: center;
  gap: 10px;
  font-family: var(--font-mono);
  font-size: 0.82rem;
  letter-spacing: 0.16em;
  text-transform: uppercase;
  color: var(--ink-soft);
  margin: 0 0 14px;
}

.seal {
  display: inline-flex;
  align-items: center;
  justify-content: center;
  width: 26px;
  height: 26px;
  border-radius: 6px;
  background: var(--accent);
  color: var(--card);
  font-family: var(--font-serif);
  font-size: 0.88rem;
  letter-spacing: 0;
  text-transform: none;
  box-shadow: var(--shadow-soft);
}

.section-head h2 {
  font-size: clamp(1.5rem, 3vw, 2.15rem);
  margin: 0 0 12px;
}

.section-intro {
  color: var(--ink-soft);
  font-size: 1.05rem;
  max-width: 62ch;
  margin: 0;
}

/* ---------- 特性卡片 ---------- */
.feature-grid {
  display: grid;
  grid-template-columns: repeat(auto-fit, minmax(300px, 1fr));
  gap: 18px;
}

.feature-card {
  background: var(--card);
  border: 1px solid var(--line);
  border-radius: var(--radius);
  padding: 26px 24px 22px;
  box-shadow: var(--shadow-soft);
  transition: transform 0.18s ease, box-shadow 0.18s ease;
}

.feature-card:hover {
  transform: translateY(-4px);
  box-shadow: var(--shadow-card);
}

.feature-tile {
  display: inline-flex;
  align-items: center;
  justify-content: center;
  width: 46px;
  height: 46px;
  border-radius: 12px;
  background: var(--accent-soft);
  border: 1px solid rgba(185, 58, 34, 0.22);
  color: var(--accent-deep);
  font-family: var(--font-serif);
  font-size: 1.3rem;
  margin-bottom: 16px;
}

.feature-card h3 { font-size: 1.18rem; margin-bottom: 8px; }
.feature-card p { color: var(--ink-soft); font-size: 0.97rem; margin: 0; }

/* ---------- 流程步骤 ---------- */
.flow-steps {
  list-style: none;
  margin: 0;
  padding: 0;
  display: grid;
  grid-template-columns: repeat(auto-fit, minmax(190px, 1fr));
  gap: 16px;
  counter-reset: step;
}

.flow-step {
  background: var(--card);
  border: 1px solid var(--line);
  border-radius: var(--radius);
  padding: 20px 18px;
  position: relative;
}

.flow-num {
  display: block;
  font-family: var(--font-mono);
  font-size: 1.5rem;
  font-weight: 700;
  color: var(--accent);
  margin-bottom: 10px;
}

.flow-step h3 { font-size: 1.05rem; margin-bottom: 6px; }
.flow-step p { font-size: 0.92rem; color: var(--ink-soft); margin: 0; }

/* ---------- 状态条 ---------- */
.status-strip {
  display: flex;
  align-items: center;
  gap: 10px;
  flex-wrap: wrap;
  background: var(--ink);
  color: var(--paper);
  border-radius: 12px;
  padding: 14px 20px;
  font-size: 0.98rem;
  margin: 0 0 40px;
}

.status-strip .status-dot { animation: none; background: #e8b04b; flex: none; }

/* ---------- 时间线 ---------- */
.timeline {
  list-style: none;
  margin: 0 0 52px;
  padding: 0;
  border-left: 2px solid var(--line);
}

.timeline-item {
  position: relative;
  padding: 0 0 30px 30px;
}
.timeline-item:last-child { padding-bottom: 0; }

.timeline-item::before {
  content: "";
  position: absolute;
  left: -7px;
  top: 7px;
  width: 12px;
  height: 12px;
  border-radius: 50%;
  background: var(--paper);
  border: 3px solid var(--accent);
}

.timeline-meta {
  display: flex;
  align-items: center;
  gap: 12px;
  margin-bottom: 8px;
}

.version-badge {
  font-family: var(--font-mono);
  font-size: 0.82rem;
  font-weight: 700;
  color: var(--card);
  background: var(--accent);
  border-radius: 7px;
  padding: 2px 10px;
}

.timeline-meta time {
  font-family: var(--font-mono);
  font-size: 0.8rem;
  color: var(--ink-faint);
}

.timeline-item h3 { font-size: 1.12rem; margin-bottom: 6px; }
.timeline-item p { color: var(--ink-soft); font-size: 0.97rem; margin: 0; max-width: 68ch; }

/* ---------- 工程实践 ---------- */
.practice-title {
  font-size: 1.3rem;
  margin-bottom: 18px;
}

.practice-grid {
  display: grid;
  grid-template-columns: repeat(auto-fit, minmax(260px, 1fr));
  gap: 16px;
}

.practice-card {
  background: var(--card);
  border: 1px solid var(--line);
  border-left: 4px solid var(--accent);
  border-radius: 10px;
  padding: 18px 20px;
}

.practice-card h4 {
  font-family: var(--font-sans);
  font-size: 0.95rem;
  font-weight: 700;
  margin-bottom: 6px;
}

.practice-card p { font-size: 0.92rem; color: var(--ink-soft); margin: 0; }

/* ---------- FAQ ---------- */
.faq-list { display: grid; gap: 12px; }

.faq-item {
  background: var(--card);
  border: 1px solid var(--line);
  border-radius: 12px;
  padding: 4px 6px;
}

.faq-item summary {
  display: flex;
  align-items: center;
  gap: 10px;
  cursor: pointer;
  list-style: none;
  padding: 14px 16px;
  font-family: var(--font-serif);
  font-weight: 700;
  font-size: 1.05rem;
}

.faq-item summary::-webkit-details-marker { display: none; }

.faq-mark {
  margin-left: auto;
  flex: none;
  position: relative;
  width: 18px;
  height: 18px;
}
.faq-mark::before, .faq-mark::after {
  content: "";
  position: absolute;
  top: 50%;
  left: 50%;
  width: 12px;
  height: 2px;
  border-radius: 2px;
  background: var(--ink-soft);
  transform: translate(-50%, -50%);
  transition: transform 0.18s ease;
}
.faq-mark::after { transform: translate(-50%, -50%) rotate(90deg); }
.faq-item[open] .faq-mark::after { transform: translate(-50%, -50%) rotate(0deg); }

.faq-item p {
  padding: 0 16px 16px;
  color: var(--ink-soft);
  margin: 0;
  max-width: 72ch;
}

/* ---------- 页脚 ---------- */
.site-footer {
  background: var(--ink);
  color: #cfc7b6;
  padding: 56px 0 34px;
}

.footer-inner {
  display: flex;
  align-items: flex-start;
  justify-content: space-between;
  gap: 32px;
  flex-wrap: wrap;
  padding-bottom: 30px;
  border-bottom: 1px solid rgba(245, 239, 227, 0.16);
}

.footer-brand .brand-mark { background: var(--paper); color: var(--ink); }

.footer-name {
  font-family: var(--font-serif);
  font-weight: 700;
  font-size: 1.15rem;
  color: var(--paper);
  margin: 10px 0 2px;
}

.footer-status {
  font-family: var(--font-mono);
  font-size: 0.8rem;
  color: #9a917e;
  margin: 0;
}

.footer-nav {
  display: flex;
  gap: 6px;
  flex-wrap: wrap;
}

.footer-nav a {
  color: #cfc7b6;
  padding: 6px 12px;
  border-radius: 8px;
  font-size: 0.93rem;
}
.footer-nav a:hover {
  color: var(--paper);
  background: rgba(245, 239, 227, 0.1);
  text-decoration: none;
}

.footer-note {
  padding-top: 26px;
  text-align: center;
}

.footer-note p {
  font-size: 0.85rem;
  color: #9a917e;
  margin: 0 0 6px;
}

.footer-credit {
  font-family: var(--font-mono);
  letter-spacing: 0.14em;
  color: #cfc7b6;
  font-size: 0.86rem;
}

/* ---------- 响应式（移动端单栏） ---------- */
@media (max-width: 960px) {
  .hero-grid { grid-template-columns: 1fr; gap: 46px; }
  .hero { padding: 60px 0 72px; }
  .hero-visual { max-width: 520px; margin: 0 auto; width: 100%; }
}

@media (max-width: 640px) {
  .container, .container-narrow { width: calc(100% - 36px); }

  .header-inner { gap: 12px; }
  .site-nav { order: 3; width: 100%; margin-left: 0; }
  .lang-switch { margin-left: auto; }

  .hero { padding: 44px 0 56px; }
  .hero-cta .btn { width: 100%; }

  .mock-btns { gap: 7px; }
  .mock-card { padding: 20px 18px 18px; }
  .mock-word { font-size: 2.1rem; }

  .section { padding: 60px 0; }
  .timeline-item { padding-left: 24px; }
  .footer-inner { flex-direction: column; gap: 22px; }
}

/* ---------- 动效偏好 ---------- */
@media (prefers-reduced-motion: reduce) {
  html { scroll-behavior: auto; }
  *, *::before, *::after {
    animation-duration: 0.001s !important;
    animation-iteration-count: 1 !important;
    transition-duration: 0.001s !important;
  }
  .btn:hover, .feature-card:hover { transform: none; }
}