/* ============================================================
   AI 大模型导航 — 样式表（白色主题）
   目录结构：index.html / style.css / script.js / model.jpg
   ============================================================ */

/* ---------- 设计变量 ---------- */
:root{
  --bg:#f5f6fa;                 /* 页面底色（浅灰白） */
  --card:#ffffff;               /* 卡片底色（纯白） */
  --border:#e6e8f2;             /* 描边 */
  --text:#191d33;               /* 主文字 */
  --text-dim:#5c6383;           /* 次要文字 */
  --accent1:#6366f1;            /* 主题色 1（靛蓝） */
  --accent2:#a855f7;            /* 主题色 2（紫） */
  --accent3:#ec4899;            /* 主题色 3（粉） */
  --shadow-sm:0 2px 10px rgba(24,28,54,.06);
  --shadow-md:0 14px 40px rgba(24,28,54,.12);
  --radius:18px;
}

/* ---------- 基础 ---------- */
*{margin:0;padding:0;box-sizing:border-box}
html{scroll-behavior:smooth}
body{
  font-family:"PingFang SC","Microsoft YaHei","Segoe UI",system-ui,-apple-system,sans-serif;
  background:var(--bg);
  color:var(--text);
  line-height:1.6;
  overflow-x:hidden;
  -webkit-font-smoothing:antialiased;
}
a{text-decoration:none;color:inherit}
::selection{background:rgba(99,102,241,.22)}
a:focus-visible,button:focus-visible{outline:2px solid var(--accent1);outline-offset:2px;border-radius:6px}

/* 背景装饰光斑 */
.bg-decor{
  position:fixed;inset:0;z-index:-1;pointer-events:none;
  background:
    radial-gradient(700px 460px at 12% -5%, rgba(99,102,241,.10), transparent 60%),
    radial-gradient(800px 520px at 95% 10%, rgba(168,85,247,.09), transparent 60%),
    radial-gradient(700px 600px at 50% 110%, rgba(236,72,153,.07), transparent 60%);
}

/* 页面内容容器；注意：与 .wrap 同用的 .hero/.section/.foot-inner 只能写 padding-top/bottom，
   若写 padding 简写（如 padding:54px 0 10px）会把这里的左右 24px 覆盖成 0，导致手机端顶到屏幕边 */
.wrap{max-width:1200px;margin:0 auto;padding:0 24px}

/* ---------- 各模型品牌色（卡片图标渐变用） ---------- */
.c-chatgpt  {--c1:#10a37f;--c2:#0b8f6d}
.c-gemini   {--c1:#4b8bf5;--c2:#9b5de5}
.c-claude   {--c1:#d97757;--c2:#b3552f}
.c-grok     {--c1:#454b58;--c2:#1b1f28}

/* ---------- 顶部导航 ---------- */
.site-header{
  position:sticky;top:0;z-index:50;
  background:rgba(255,255,255,.85);
  backdrop-filter:blur(14px);-webkit-backdrop-filter:blur(14px);
  border-bottom:1px solid var(--border);
  transition:box-shadow .25s;
}
.site-header.scrolled{box-shadow:var(--shadow-sm)}
.header-inner{display:flex;align-items:center;justify-content:space-between;height:64px}
.logo{display:flex;align-items:center;gap:10px;font-size:19px;font-weight:700;letter-spacing:.5px;color:var(--text)}
.logo svg{width:26px;height:26px;flex:none}

/* ---------- 首屏 Hero ---------- */
.hero{display:flex;align-items:center;gap:56px;padding-top:72px;padding-bottom:60px;flex-wrap:wrap}
.hero-text{flex:1 1 420px;min-width:300px}
.badge{
  display:inline-flex;align-items:center;gap:8px;
  font-size:13px;color:#7c3aed;letter-spacing:2px;font-weight:600;
  border:1px solid rgba(124,58,237,.25);background:rgba(124,58,237,.07);
  padding:6px 16px;border-radius:999px;margin-bottom:22px;
}
.badge::before{
  content:"";width:7px;height:7px;border-radius:50%;background:#7c3aed;
  box-shadow:0 0 10px rgba(124,58,237,.8);animation:pulse 2s infinite;
}
@keyframes pulse{0%,100%{opacity:1}50%{opacity:.3}}
.hero h1{font-size:clamp(34px,5vw,54px);line-height:1.18;font-weight:800;letter-spacing:1px}
.hero h1 em{
  font-style:normal;
  background:linear-gradient(90deg,var(--accent1),var(--accent2),var(--accent3));
  -webkit-background-clip:text;background-clip:text;-webkit-text-fill-color:transparent;
}
.hero p{margin:20px 0 30px;color:var(--text-dim);font-size:16.5px;max-width:520px}

/* 首屏图片：保持 model.jpg 原始 16:9 比例，不裁剪、不压缩变形 */
.hero-img{flex:1 1 420px;min-width:300px;position:relative}
.hero-img::before{
  content:"";position:absolute;inset:-10px;border-radius:26px;z-index:-1;
  background:linear-gradient(135deg,rgba(99,102,241,.28),rgba(236,72,153,.2));
  filter:blur(36px);opacity:.75;
}
.hero-img img{
  width:100%;height:auto;display:block;      /* height:auto 保证按原始比例缩放 */
  border-radius:20px;
  border:1px solid var(--border);
  box-shadow:var(--shadow-md);
  background:#fff;
}

/* ---------- 区块标题 ---------- */
.section{padding-top:54px;padding-bottom:10px}
.section-head{display:flex;align-items:baseline;gap:16px;margin-bottom:30px;flex-wrap:wrap}
.section-head h2{font-size:27px;font-weight:800;letter-spacing:.5px}
.section-head h2::before{content:"▍";color:var(--accent2);margin-right:4px}
.section-head span{color:var(--text-dim);font-size:14px}

/* ---------- 卡片网格（便捷入口 / 旗舰模型共用） ---------- */
.grid-cards{display:grid;grid-template-columns:repeat(2,1fr);gap:24px}
.f-card{
  position:relative;
  background:var(--card);border:1px solid var(--border);border-radius:20px;
  padding:30px 30px 28px;overflow:hidden;box-shadow:var(--shadow-sm);
  transition:transform .25s,box-shadow .25s,border-color .25s;
}
/* 悬停时品牌色淡晕 */
.f-card::before{
  content:"";position:absolute;inset:0;pointer-events:none;
  background:radial-gradient(460px 220px at 15% 0%,color-mix(in srgb,var(--c1) 8%,transparent),transparent 70%);
  opacity:0;transition:opacity .3s;
}
.f-card:hover::before{opacity:1}
/* 顶部品牌渐变条 */
.f-card::after{
  content:"";position:absolute;top:0;left:0;right:0;height:3px;
  background:linear-gradient(90deg,var(--c1),var(--c2));
  opacity:0;transition:opacity .25s;
}
.f-card:hover,
.reveal.visible.f-card:hover{   /* 提升特异性，避免被渐显结束的 transform:none 覆盖 */
  transform:translateY(-6px);
  border-color:color-mix(in srgb,var(--c1) 45%,#fff);
  box-shadow:var(--shadow-md);
}
.f-card:hover::after{opacity:1}
/* 链接铺满整卡，内部网格分区：图标在左、文字在右 */
.f-card > a{
  display:grid;height:100%;
  grid-template-columns:auto 1fr;
  grid-template-areas:
    "icon head"
    "icon desc"
    "icon meta"
    "icon cta";
  column-gap:24px;row-gap:8px;align-items:center;
}
.f-icon{
  grid-area:icon;align-self:start;
  width:68px;height:68px;border-radius:18px;display:grid;place-items:center;
  background:linear-gradient(135deg,#fff,color-mix(in srgb,var(--c1) 7%,#fff));
  border:1px solid var(--border);box-shadow:var(--shadow-sm);
  transition:transform .25s;
}
.f-card:hover .f-icon{transform:scale(1.06)}
.f-icon svg,.f-icon span{width:36px;height:36px;color:var(--c1);font-size:26px;font-weight:800;line-height:1}
.f-icon img{width:36px;height:36px;object-fit:contain;display:block}
.f-card h3{grid-area:head;font-size:20px;display:flex;align-items:center;gap:8px;flex-wrap:wrap}
.f-card h3 small{
  font-size:12px;font-weight:500;color:var(--text-dim);
  border:1px solid var(--border);background:#f6f7fb;border-radius:6px;padding:2px 9px;
}
.f-card p{grid-area:desc;font-size:14.5px;line-height:1.75;color:var(--text-dim)}
.chips{grid-area:meta;display:flex;gap:8px;flex-wrap:wrap;margin-top:6px}
.chips i{font-style:normal;font-size:12px;color:#4a5070;background:#f1f2f9;border-radius:6px;padding:3px 10px}
.f-link{grid-area:cta;justify-self:start;align-self:end;display:inline-flex;align-items:center;gap:6px;font-size:14.5px;font-weight:600;color:var(--c2);margin-top:10px;transition:gap .2s}
.f-card:hover .f-link{gap:10px}

/* ---------- 便捷入口提示文案 ---------- */
.q-note{margin-top:14px;font-size:12.5px;color:var(--text-dim);line-height:1.6}

/* ---------- 返回顶部 ---------- */
#backTop{
  position:fixed;right:24px;bottom:24px;z-index:60;
  width:44px;height:44px;border-radius:50%;border:1px solid var(--border);
  background:#fff;color:var(--text-dim);font-size:18px;cursor:pointer;
  box-shadow:var(--shadow-sm);
  opacity:0;visibility:hidden;transform:translateY(10px);
  transition:opacity .3s,transform .3s,visibility .3s,color .2s,border-color .2s;
}
#backTop.show{opacity:1;visibility:visible;transform:none}
#backTop:hover{color:var(--accent1);border-color:#c3c8ee}

/* ---------- 页脚 ---------- */
footer{margin-top:70px;background:#fff;border-top:1px solid var(--border)}
.foot-inner{display:flex;justify-content:space-between;align-items:center;gap:18px;flex-wrap:wrap;padding-top:30px;padding-bottom:38px}
footer p{font-size:13px;color:var(--text-dim)}
footer p b{color:#6d28d9;font-weight:600}

/* ---------- 滚动渐显（无 JS 时默认全部可见） ---------- */
html.js .reveal{opacity:0;transform:translateY(24px);transition:opacity .6s ease,transform .6s ease}
html.js .reveal.visible{opacity:1;transform:none}
@media (prefers-reduced-motion:reduce){
  html.js .reveal{opacity:1;transform:none;transition:none}
}

/* ---------- 响应式 ---------- */
@media (max-width:640px){
  .hero{padding-top:48px;padding-bottom:40px;gap:36px}
  .hero-img::before{inset:0}              /* 收敛装饰光斑，避免窄屏横向溢出 */
  .grid-cards{grid-template-columns:1fr}
  .f-card{padding:24px 22px 22px}
  .f-card > a{
    grid-template-columns:1fr;
    grid-template-areas:
      "icon"
      "head"
      "desc"
      "meta"
      "cta";
    column-gap:0;row-gap:12px;
  }
  .f-icon{width:56px;height:56px;border-radius:15px}
  .f-icon svg,.f-icon span{width:30px;height:30px;font-size:22px}
  .f-icon img{width:30px;height:30px}
}