/* ==========================================================================
   纳渊护学 · 官网样式
   设计语言与「纳渊英语」官网保持一致（同一套排版节奏与组件），
   仅把主色从品牌绿换成纳渊护学的靛蓝，让三个产品看起来是一家人。
   ========================================================================== */

:root{
  --brand:#2E6BE6;
  --brand-dark:#1D4FB0;
  --brand-light:#EEF3FF;
  --brand-line:#D7E2FB;
  --accent:#FFB020;

  --ink:#141A26;
  --body:#3B4351;
  --muted:#6B7280;
  --line:#E6EBF3;

  --bg:#FFFFFF;
  --bg-soft:#F7F9FD;

  --radius:16px;
  --radius-lg:24px;
  --shadow:0 1px 2px rgba(20,26,38,.04), 0 12px 32px rgba(20,26,38,.06);
}

*{box-sizing:border-box}
html{scroll-behavior:smooth}
body{
  margin:0;
  background:var(--bg);
  color:var(--body);
  font:16px/1.75 -apple-system,BlinkMacSystemFont,"PingFang SC","Hiragino Sans GB","Microsoft YaHei",sans-serif;
  -webkit-font-smoothing:antialiased;
}
a{color:var(--brand);text-decoration:none}
a:hover{text-decoration:underline}
img{max-width:100%;display:block}

.wrap{max-width:1080px;margin:0 auto;padding:0 24px}

/* ---------------- 顶部导航 ---------------- */
.nav{
  position:sticky;top:0;z-index:50;
  background:rgba(255,255,255,.88);
  backdrop-filter:saturate(180%) blur(12px);
  border-bottom:1px solid var(--line);
}
.nav-inner{
  max-width:1080px;margin:0 auto;padding:12px 24px;
  display:flex;align-items:center;gap:24px;
}
.brand{display:flex;align-items:center;gap:10px;font-weight:800;color:var(--ink);font-size:18px;letter-spacing:.2px}
.brand:hover{text-decoration:none}
.brand img{width:34px;height:34px;border-radius:8px}
.brand small{display:block;font-size:11px;font-weight:500;color:var(--muted);letter-spacing:2px}
.nav-links{display:flex;gap:22px;margin-left:auto;font-size:15px}
.nav-links a{color:var(--body)}
.nav-links a:hover{color:var(--brand);text-decoration:none}
.btn{
  display:inline-flex;align-items:center;justify-content:center;gap:8px;
  padding:11px 22px;border-radius:12px;font-weight:650;font-size:15px;
  border:1px solid transparent;cursor:pointer;transition:.18s ease;
}
.btn-primary{background:var(--brand);color:#fff;box-shadow:0 8px 20px rgba(46,107,230,.24)}
.btn-primary:hover{background:var(--brand-dark);text-decoration:none;transform:translateY(-1px)}
.btn-ghost{background:#fff;color:var(--ink);border-color:var(--line)}
.btn-ghost:hover{border-color:var(--brand-line);background:var(--brand-light);text-decoration:none}

@media (max-width:820px){
  .nav-links{display:none}
}

/* ---------------- Hero ---------------- */
.hero{padding:72px 0 56px;background:
  radial-gradient(900px 420px at 78% -10%, var(--brand-light), transparent 70%),
  linear-gradient(180deg,#fff, var(--bg-soft));
}
.hero-inner{display:grid;grid-template-columns:1.05fr .95fr;gap:56px;align-items:center}
.tag{
  display:inline-flex;align-items:center;gap:8px;
  background:var(--brand-light);color:var(--brand-dark);
  border:1px solid var(--brand-line);
  padding:5px 14px;border-radius:999px;font-size:13px;font-weight:650;
}
h1{
  font-size:46px;line-height:1.24;margin:20px 0 0;
  color:var(--ink);letter-spacing:-.5px;font-weight:800;
}
h1 em{font-style:normal;color:var(--brand);position:relative}
.lead{font-size:17px;color:var(--body);margin:20px 0 0;max-width:33em}
.actions{display:flex;gap:12px;margin-top:28px;flex-wrap:wrap}
.note{font-size:13px;color:var(--muted);margin-top:14px}

/* 手机样机（纯 CSS，不依赖截图） */
.phone{
  width:300px;margin-left:auto;border-radius:38px;background:#0C1220;
  padding:10px;box-shadow:0 30px 70px rgba(12,18,32,.28);position:relative;
}
.phone::after{
  content:"";position:absolute;left:50%;bottom:16px;transform:translateX(-50%);
  width:110px;height:4px;border-radius:99px;background:rgba(255,255,255,.35)
}
.screen{background:#F7F9FC;border-radius:30px;overflow:hidden;min-height:520px;padding:18px 16px 26px}
.screen-top{display:flex;align-items:center;justify-content:space-between;font-size:12px;color:var(--muted);padding:0 4px 14px}
.screen-top b{color:var(--brand);font-size:12px;letter-spacing:.5px}
.q-card{background:#fff;border:1px solid var(--line);border-radius:18px;padding:16px;box-shadow:var(--shadow)}
.q-meta{font-size:11px;color:var(--muted);display:flex;justify-content:space-between;margin-bottom:10px}
.q-text{font-size:17px;font-weight:750;color:var(--ink);line-height:1.5}
.q-passage{margin-top:10px;background:#F3F6FB;border-radius:10px;padding:10px;font-size:12px;color:#4A5568;line-height:1.7}
.q-input{margin-top:14px;border:1px solid var(--line);border-radius:10px;padding:11px 12px;font-size:13px;color:#9AA3AF}
.q-input.caret{border-color:var(--brand);color:var(--ink)}
.q-btn{margin-top:12px;background:var(--brand);color:#fff;text-align:center;border-radius:10px;padding:12px;font-size:14px;font-weight:650}
.q-foot{display:flex;justify-content:space-between;margin-top:12px;font-size:11px;color:var(--muted)}
.q-good{color:#16A34A;font-weight:700}

/* ---------------- 通用板块 ---------------- */
section{padding:72px 0}
.section-soft{background:var(--bg-soft);border-top:1px solid var(--line);border-bottom:1px solid var(--line)}
.section-head{max-width:640px;margin:0 auto 40px;text-align:center}
.section-head .kicker{font-size:13px;letter-spacing:2px;color:var(--brand);font-weight:700}
.section-head h2{font-size:32px;line-height:1.35;margin:12px 0 0;color:var(--ink);font-weight:800;letter-spacing:-.3px}
.section-head p{margin:14px 0 0;color:var(--muted)}

.grid-3{display:grid;grid-template-columns:repeat(3,1fr);gap:20px}
.grid-4{display:grid;grid-template-columns:repeat(2,1fr);gap:20px}
.card{
  background:#fff;border:1px solid var(--line);border-radius:var(--radius);
  padding:26px 24px;box-shadow:var(--shadow);
}
.card h3{margin:0 0 10px;font-size:18px;color:var(--ink);font-weight:750}
.card p{margin:0;color:var(--body);font-size:15px}
.card .ico{
  width:40px;height:40px;border-radius:12px;background:var(--brand-light);
  color:var(--brand);display:flex;align-items:center;justify-content:center;
  font-weight:800;font-size:16px;margin-bottom:16px;
}

.num-card{position:relative;padding-top:22px}
.num-card .num{
  font-size:13px;font-weight:800;color:var(--brand);letter-spacing:1px;
  display:block;margin-bottom:10px;
}
.num-card::before{
  content:"";position:absolute;left:0;top:0;width:36px;height:3px;
  border-radius:99px;background:var(--brand);
}

/* 步骤 */
.steps{display:grid;grid-template-columns:repeat(4,1fr);gap:18px}
.step{background:#fff;border:1px solid var(--line);border-radius:var(--radius);padding:22px;box-shadow:var(--shadow)}
.step .idx{
  width:30px;height:30px;border-radius:50%;background:var(--brand);color:#fff;
  display:flex;align-items:center;justify-content:center;font-size:14px;font-weight:800;margin-bottom:14px;
}
.step h4{margin:0 0 8px;font-size:16px;color:var(--ink)}
.step p{margin:0;font-size:14px;color:var(--muted)}

/* 题库 */
.packs{display:grid;grid-template-columns:repeat(3,1fr);gap:16px}
.pack{background:#fff;border:1px solid var(--line);border-radius:14px;padding:18px;display:flex;gap:14px;align-items:flex-start}
.pack .dot{width:10px;height:10px;border-radius:50%;background:var(--brand);margin-top:9px;flex:none}
.pack b{display:block;color:var(--ink);font-size:15px}
.pack span{font-size:13px;color:var(--muted)}
.chips{display:flex;gap:10px;flex-wrap:wrap;margin-bottom:26px;justify-content:center}
.chip{
  padding:7px 16px;border-radius:999px;border:1px solid var(--line);
  background:#fff;font-size:14px;color:var(--body);
}
.chip.on{background:var(--brand);border-color:var(--brand);color:#fff;font-weight:650}

/* FAQ */
.faq{max-width:780px;margin:0 auto}
details{
  background:#fff;border:1px solid var(--line);border-radius:14px;
  padding:18px 22px;margin-bottom:12px;box-shadow:var(--shadow);
}
details[open]{border-color:var(--brand-line)}
summary{
  cursor:pointer;font-weight:700;color:var(--ink);font-size:16px;
  list-style:none;display:flex;justify-content:space-between;align-items:center;gap:16px;
}
summary::-webkit-details-marker{display:none}
summary::after{content:"+";color:var(--brand);font-size:20px;font-weight:400}
details[open] summary::after{content:"−"}
details p{margin:12px 0 0;color:var(--body);font-size:15px}

/* 下载区 */
.cta{
  background:linear-gradient(135deg,#2E6BE6,#1740A8);
  border-radius:var(--radius-lg);padding:48px 40px;color:#fff;
  display:flex;align-items:center;gap:32px;justify-content:space-between;flex-wrap:wrap;
  box-shadow:0 24px 60px rgba(29,79,176,.28);
}
.cta h2{margin:0;font-size:28px;color:#fff;font-weight:800}
.cta p{margin:10px 0 0;color:rgba(255,255,255,.82);font-size:15px}
.cta .btn-primary{background:#fff;color:var(--brand-dark);box-shadow:none}
.cta .btn-primary:hover{background:#F2F6FF;color:var(--brand-dark)}
.cta .btn-ghost{background:transparent;color:#fff;border-color:rgba(255,255,255,.4)}
.cta .btn-ghost:hover{background:rgba(255,255,255,.12);color:#fff}

/* 页脚 */
footer{background:#0F1526;color:#94A3B8;padding:52px 0 32px;font-size:14px}
.foot-top{display:flex;justify-content:space-between;gap:40px;flex-wrap:wrap;padding-bottom:32px;border-bottom:1px solid rgba(255,255,255,.08)}
.foot-brand{display:flex;gap:14px;align-items:flex-start;max-width:340px}
.foot-brand img{width:40px;height:40px;border-radius:12px}
.foot-brand b{color:#fff;font-size:16px;display:block}
.foot-brand p{margin:8px 0 0;color:#94A3B8;font-size:13px;line-height:1.7}
.foot-links{display:grid;grid-template-columns:repeat(3,auto);gap:12px 56px}
.foot-links a{color:#94A3B8;display:block;padding:3px 0}
.foot-links a:hover{color:#fff;text-decoration:none}
.foot-links h5{margin:0 0 10px;color:#fff;font-size:13px;letter-spacing:1px;font-weight:700}
.foot-bottom{padding-top:22px;display:flex;justify-content:space-between;gap:16px;flex-wrap:wrap;font-size:12.5px;color:#64748B}
.foot-bottom a{color:#64748B}

/* 文档页（隐私政策 / 用户协议） */
.doc{max-width:820px;margin:0 auto;padding:56px 0 80px}
.doc h1{font-size:32px;margin:0 0 8px}
.doc .meta{color:var(--muted);font-size:13px;margin-bottom:36px}
.doc h2{font-size:19px;color:var(--ink);margin:36px 0 12px;font-weight:750}
.doc h3{font-size:16px;color:var(--ink);margin:22px 0 8px;font-weight:700}
.doc p,.doc li{font-size:15px;color:var(--body);line-height:1.85}
.doc ul{padding-left:22px}
.doc .callout{
  background:var(--brand-light);border:1px solid var(--brand-line);
  border-radius:12px;padding:16px 18px;margin:20px 0;font-size:14.5px;
}

/* 响应式 */
@media (max-width:960px){
  .hero-inner{grid-template-columns:1fr;gap:40px}
  .phone{margin:0 auto}
  .grid-3,.grid-4,.steps,.packs{grid-template-columns:1fr}
  h1{font-size:34px}
  .section-head h2{font-size:25px}
  .cta{padding:34px 26px}
  section{padding:52px 0}
}
@media (min-width:641px) and (max-width:960px){
  .grid-3,.grid-4{grid-template-columns:repeat(2,1fr)}
  .steps{grid-template-columns:repeat(2,1fr)}
  .packs{grid-template-columns:repeat(2,1fr)}
}