/* ===== AI辅导 aifudao123.com landing ===== */

:root {
  --ink: #1c2333;
  --ink-soft: #4b5568;
  --ink-faint: #8a93a6;
  --brand: #2f5fe0;
  --brand-dark: #234bb8;
  --brand-tint: #eef3ff;
  --accent: #c4493a;
  --paper: #ffffff;
  --paper-alt: #f6f8fc;
  --line: #e4e9f2;
  --radius: 14px;
  --shadow: 0 10px 30px rgba(28, 35, 51, 0.08);
  --font: "PingFang SC", "Hiragino Sans GB", "Microsoft YaHei", "Noto Sans SC",
          -apple-system, "Segoe UI", sans-serif;
}

* { margin: 0; padding: 0; box-sizing: border-box; }

html { scroll-behavior: smooth; }

body {
  font-family: var(--font);
  color: var(--ink);
  background: var(--paper);
  line-height: 1.7;
  -webkit-font-smoothing: antialiased;
}

.container {
  max-width: 1100px;
  margin: 0 auto;
  padding: 0 24px;
}

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

h1, h2, h3 { line-height: 1.3; font-weight: 700; }

.center { text-align: center; }

/* ----- buttons ----- */
.btn {
  display: inline-block;
  border-radius: 999px;
  font-weight: 600;
  text-decoration: none !important;
  transition: transform 0.15s ease, box-shadow 0.15s ease, background 0.15s ease;
  white-space: nowrap;
}
.btn:hover { transform: translateY(-1px); }
.btn-primary {
  background: var(--brand);
  color: #fff;
  box-shadow: 0 6px 18px rgba(47, 95, 224, 0.35);
}
.btn-primary:hover { background: var(--brand-dark); }
.btn-ghost {
  color: var(--brand);
  border: 1.5px solid var(--brand);
  background: transparent;
}
.btn-invert {
  background: #fff;
  color: var(--brand-dark);
}
.btn-sm { padding: 8px 20px; font-size: 14px; }
.btn-lg { padding: 14px 34px; font-size: 17px; }

/* ----- header ----- */
.site-header {
  position: sticky;
  top: 0;
  z-index: 50;
  background: rgba(255, 255, 255, 0.92);
  backdrop-filter: blur(10px);
  border-bottom: 1px solid var(--line);
}
.header-inner {
  display: flex;
  align-items: center;
  gap: 28px;
  height: 64px;
}
.brand {
  display: flex;
  align-items: center;
  gap: 10px;
  text-decoration: none !important;
  color: var(--ink);
}
.brand img { border-radius: 8px; }
.brand-name { font-weight: 700; font-size: 18px; }
.brand-name small { color: var(--ink-faint); font-weight: 500; font-size: 12px; }
.site-nav {
  display: flex;
  gap: 22px;
  margin-left: auto;
}
.site-nav a {
  color: var(--ink-soft);
  font-size: 15px;
}
.site-nav a:hover { color: var(--brand); text-decoration: none; }

/* ----- hero ----- */
.hero {
  background:
    radial-gradient(900px 420px at 85% -10%, rgba(47, 95, 224, 0.14), transparent 60%),
    radial-gradient(700px 380px at -10% 30%, rgba(196, 73, 58, 0.08), transparent 55%),
    var(--paper);
  padding: 84px 0 72px;
}
.hero-inner {
  display: grid;
  grid-template-columns: 1.15fr 1fr;
  gap: 48px;
  align-items: center;
}
.eyebrow {
  color: var(--brand);
  font-weight: 700;
  letter-spacing: 0.18em;
  font-size: 14px;
  margin-bottom: 14px;
}
.hero h1 {
  font-size: 44px;
  margin-bottom: 20px;
}
.hero h1 em {
  font-style: normal;
  color: var(--brand);
}
.lead {
  font-size: 18px;
  color: var(--ink-soft);
  margin-bottom: 30px;
  max-width: 34em;
}
.hero-actions { display: flex; gap: 14px; flex-wrap: wrap; }
.hero-note {
  margin-top: 16px;
  color: var(--ink-faint);
  font-size: 14px;
}

/* hero demo card */
.hero-demo { position: relative; }
.demo-card {
  background: #fff;
  border: 1px solid var(--line);
  border-radius: var(--radius);
  box-shadow: var(--shadow);
  padding: 22px;
}
.demo-search {
  display: flex;
  gap: 10px;
  margin-bottom: 18px;
}
.demo-input {
  flex: 1;
  border: 1.5px solid var(--line);
  border-radius: 10px;
  padding: 10px 14px;
  color: var(--ink-soft);
  font-size: 15px;
  background: var(--paper-alt);
}
.demo-btn {
  background: var(--brand);
  color: #fff;
  border-radius: 10px;
  padding: 10px 18px;
  font-weight: 700;
}
.demo-headword { font-size: 22px; font-weight: 700; }
.demo-phonetic { color: var(--ink-faint); font-weight: 400; font-size: 15px; margin-left: 6px; }
.demo-def { color: var(--ink-soft); margin: 6px 0 14px; }
.demo-tags { display: flex; gap: 8px; flex-wrap: wrap; margin-bottom: 16px; }
.demo-tags span {
  background: var(--brand-tint);
  color: var(--brand-dark);
  border-radius: 8px;
  padding: 4px 10px;
  font-size: 13px;
  font-weight: 600;
}
.demo-score { display: flex; align-items: center; gap: 10px; }
.demo-score-label { font-size: 13px; color: var(--ink-faint); }
.demo-score-bar {
  flex: 1;
  height: 8px;
  background: var(--line);
  border-radius: 99px;
  overflow: hidden;
}
.demo-score-bar i {
  display: block;
  height: 100%;
  background: linear-gradient(90deg, #37b26c, #6fd49a);
  border-radius: 99px;
}
.demo-score-num { font-weight: 800; color: #2c8f57; }
.demo-chip {
  position: absolute;
  background: #fff;
  border: 1px solid var(--line);
  border-radius: 99px;
  box-shadow: var(--shadow);
  padding: 8px 16px;
  font-size: 13px;
  font-weight: 600;
  color: var(--ink-soft);
}
.demo-chip-1 { top: -16px; right: 8px; color: #2c8f57; }
.demo-chip-2 { bottom: -16px; left: 12px; color: var(--brand-dark); }

/* ----- stats strip ----- */
.stats-strip {
  border-top: 1px solid var(--line);
  border-bottom: 1px solid var(--line);
  background: var(--paper-alt);
}
.stats-inner {
  display: grid;
  grid-template-columns: repeat(4, 1fr);
  gap: 16px;
  padding: 22px 24px;
}
.stat { text-align: center; }
.stat strong { display: block; font-size: 18px; color: var(--ink); }
.stat span { font-size: 13px; color: var(--ink-faint); }

/* ----- sections ----- */
.section { padding: 76px 0; }
.section-alt { background: var(--paper-alt); }
.section h2 {
  font-size: 30px;
  text-align: center;
  margin-bottom: 14px;
}
.section-lead {
  text-align: center;
  color: var(--ink-soft);
  max-width: 40em;
  margin: 0 auto 44px;
}

/* features */
.feature-grid {
  display: grid;
  grid-template-columns: repeat(3, 1fr);
  gap: 22px;
}
.feature {
  background: #fff;
  border: 1px solid var(--line);
  border-radius: var(--radius);
  padding: 26px 24px;
  transition: box-shadow 0.2s ease, transform 0.2s ease;
}
.feature:hover { box-shadow: var(--shadow); transform: translateY(-3px); }
.feature-icon { font-size: 28px; margin-bottom: 12px; }
.feature h3 { font-size: 18px; margin-bottom: 8px; }
.feature p { color: var(--ink-soft); font-size: 15px; }

/* wordlists */
.wordlist-grid {
  display: grid;
  grid-template-columns: repeat(3, 1fr);
  gap: 22px;
}
.wordlist-card {
  background: #fff;
  border: 1px solid var(--line);
  border-top: 4px solid var(--brand);
  border-radius: var(--radius);
  padding: 26px 24px;
}
.wordlist-card:nth-child(2) { border-top-color: var(--accent); }
.wordlist-card:nth-child(3) { border-top-color: #2c8f57; }
.wordlist-card h3 { font-size: 19px; margin-bottom: 10px; }
.wordlist-card p { color: var(--ink-soft); font-size: 15px; margin-bottom: 14px; }
.pill {
  display: inline-block;
  background: var(--brand-tint);
  color: var(--brand-dark);
  font-size: 13px;
  font-weight: 600;
  border-radius: 99px;
  padding: 4px 14px;
}

/* pricing */
.pricing-grid {
  display: grid;
  grid-template-columns: repeat(3, 1fr);
  gap: 22px;
  align-items: stretch;
  margin-bottom: 28px;
}
.price-card {
  position: relative;
  background: #fff;
  border: 1px solid var(--line);
  border-radius: var(--radius);
  padding: 30px 26px;
  text-align: center;
  display: flex;
  flex-direction: column;
}
.price-card-featured {
  border: 2px solid var(--brand);
  box-shadow: var(--shadow);
}
.price-badge {
  position: absolute;
  top: -14px;
  left: 50%;
  transform: translateX(-50%);
  background: var(--brand);
  color: #fff;
  font-size: 13px;
  font-weight: 700;
  border-radius: 99px;
  padding: 4px 16px;
}
.price-card h3 { font-size: 19px; margin-bottom: 12px; }
.price { color: var(--ink-soft); margin-bottom: 4px; }
.price-num {
  font-size: 42px;
  font-weight: 800;
  color: var(--ink);
  line-height: 1;
}
.price-per {
  font-size: 13px;
  color: var(--ink-faint);
  margin-bottom: 18px;
}
.price-card-featured .price-per { color: var(--brand-dark); font-weight: 600; }
.price-features {
  list-style: none;
  text-align: left;
  margin: 0 auto 22px;
  color: var(--ink-soft);
  font-size: 14.5px;
  flex: 1;
}
.price-features li {
  padding-left: 22px;
  position: relative;
  margin-bottom: 8px;
}
.price-features li::before {
  content: "✓";
  position: absolute;
  left: 0;
  color: #2c8f57;
  font-weight: 700;
}
.price-card .btn { padding: 11px 26px; font-size: 15px; }

.referral-banner {
  background: linear-gradient(120deg, #fff7ed, #fff1e6);
  border: 1px solid #f3d9bd;
  border-radius: var(--radius);
  padding: 26px 30px;
}
.referral-banner h3 { font-size: 19px; margin-bottom: 8px; color: #9a4d12; }
.referral-banner p { color: #7a5230; font-size: 15px; }
.referral-banner strong { color: #c4491a; }

/* steps */
.steps {
  display: grid;
  grid-template-columns: repeat(3, 1fr);
  gap: 22px;
  margin-bottom: 40px;
}
.step {
  background: #fff;
  border: 1px solid var(--line);
  border-radius: var(--radius);
  padding: 28px 24px;
  text-align: center;
}
.step-num {
  display: inline-flex;
  align-items: center;
  justify-content: center;
  width: 42px;
  height: 42px;
  border-radius: 50%;
  background: var(--brand);
  color: #fff;
  font-weight: 800;
  font-size: 18px;
  margin-bottom: 14px;
}
.step h3 { font-size: 18px; margin-bottom: 8px; }
.step p { color: var(--ink-soft); font-size: 15px; }

/* faq */
.faq-list { max-width: 760px; margin: 0 auto; }
.faq-list details {
  background: #fff;
  border: 1px solid var(--line);
  border-radius: 12px;
  padding: 18px 22px;
  margin-bottom: 12px;
}
.faq-list summary {
  cursor: pointer;
  font-weight: 600;
  font-size: 16px;
  list-style: none;
  position: relative;
  padding-right: 28px;
}
.faq-list summary::-webkit-details-marker { display: none; }
.faq-list summary::after {
  content: "+";
  position: absolute;
  right: 0;
  top: 0;
  color: var(--brand);
  font-size: 20px;
  font-weight: 700;
}
.faq-list details[open] summary::after { content: "–"; }
.faq-list details p {
  margin-top: 12px;
  color: var(--ink-soft);
  font-size: 15px;
}

/* CTA band */
.cta-band {
  background: linear-gradient(120deg, var(--brand-dark), var(--brand));
  color: #fff;
  padding: 68px 0;
}
.cta-band h2 { font-size: 28px; margin-bottom: 10px; }
.cta-band p { opacity: 0.9; margin-bottom: 26px; }

/* ----- footer ----- */
.site-footer {
  background: #171d2b;
  color: #aab3c5;
  padding: 52px 0 0;
  font-size: 14px;
}
.footer-inner {
  display: grid;
  grid-template-columns: 1.4fr 1fr 1fr;
  gap: 36px;
  padding-bottom: 36px;
}
.site-footer .brand-name { color: #fff; margin-bottom: 10px; }
.footer-title { color: #fff; font-weight: 600; margin-bottom: 10px; }
.site-footer a { color: #9db4e8; }
.footer-bottom {
  border-top: 1px solid rgba(255, 255, 255, 0.1);
  padding-top: 18px;
  padding-bottom: 22px;
  text-align: center;
  color: #6d7689;
  font-size: 13px;
}

/* ----- responsive ----- */
@media (max-width: 900px) {
  .hero-inner { grid-template-columns: 1fr; }
  .hero h1 { font-size: 34px; }
  .feature-grid, .wordlist-grid, .steps { grid-template-columns: 1fr 1fr; }
  .pricing-grid { grid-template-columns: 1fr; max-width: 420px; margin-left: auto; margin-right: auto; }
  .price-card-featured { order: -1; }
  .footer-inner { grid-template-columns: 1fr; gap: 24px; }
  .site-nav { display: none; }
}

@media (max-width: 560px) {
  .hero { padding: 56px 0 48px; }
  .hero h1 { font-size: 28px; }
  .feature-grid, .wordlist-grid, .steps { grid-template-columns: 1fr; }
  .stats-inner { grid-template-columns: 1fr 1fr; }
  .section { padding: 56px 0; }
  .brand-name small { display: none; }
}