/* ============================================================
   小天 · 初中数学自学网站 — 共享设计系统
   母题：二元一次方程组的解 = 两条直线的交点
   配色：墨蓝(主) + 青(副) + 珊瑚(强调/解) ；其余保持安静
   ============================================================ */
:root{
  --bg:#f5f8fc;
  --bg-subtle:#eef3fa;
  --panel:#ffffff;
  --card:#ffffff;
  --card-elevated:#f3f7fc;
  --line:#dce4ef;
  --line-soft:rgba(43,89,195,0.10);
  --text:#16263d;
  --text-secondary:#3a4a63;
  --muted:#6b7a93;
  --brand:#2b59c3;        /* 墨蓝 主 */
  --brand-soft:rgba(43,89,195,0.08);
  --brand-2:#0e9bad;      /* 青 副 */
  --brand-2-soft:rgba(14,155,173,0.10);
  --accent:#ff6a4d;       /* 珊瑚 强调/解（只用在交点） */
  --accent-soft:rgba(255,106,77,0.12);
  --ok:#1f9d57;
  --warn:#e08a00;
  --danger:#e23b3b;
  --radius:16px;
  --radius-sm:10px;
  --shadow-sm:0 2px 10px rgba(22,38,61,0.06);
  --shadow:0 10px 30px rgba(22,38,61,0.10);
  --shadow-lg:0 22px 60px rgba(22,38,61,0.16);
  --grid-line:rgba(43,89,195,0.05);
  --maxw:1120px;
  --font:"PingFang SC","Microsoft YaHei","Hiragino Sans GB","Source Han Sans SC",system-ui,-apple-system,"Segoe UI",Roboto,sans-serif;
  --mono:"SFMono-Regular",Consolas,"Liberation Mono",Menlo,monospace;
}

*{box-sizing:border-box;}
html{scroll-behavior:smooth;}
body{
  margin:0;
  font-family:var(--font);
  color:var(--text);
  background-color:var(--bg);
  /* 坐标纸网格背景：统一、像数学草稿纸 */
  background-image:
    linear-gradient(var(--grid-line) 1px, transparent 1px),
    linear-gradient(90deg, var(--grid-line) 1px, transparent 1px);
  background-size:26px 26px;
  line-height:1.7;
  -webkit-font-smoothing:antialiased;
}
a{color:var(--brand);text-decoration:none;}
img{max-width:100%;display:block;}
.wrap{max-width:var(--maxw);margin:0 auto;padding:0 24px;}

/* ---------- 区块标题（珊瑚小方块母题） ---------- */
.section{margin:72px 0;}
.section-head{display:flex;align-items:baseline;gap:12px;margin-bottom:8px;}
.section-head h2{
  font-size:clamp(22px,3vw,30px);
  margin:0;letter-spacing:.5px;color:var(--text);
  position:relative;padding-left:18px;
}
.section-head h2::before{
  content:"";position:absolute;left:0;top:.18em;width:9px;height:1em;
  background:var(--accent);border-radius:2px;
}
.section-sub{color:var(--muted);margin:0 0 28px 18px;font-size:15px;}

/* ---------- 导航 ---------- */
.nav{
  position:sticky;top:0;z-index:50;
  background:rgba(255,255,255,0.86);
  backdrop-filter:saturate(180%) blur(12px);
  border-bottom:1px solid var(--line);
}
.nav-inner{max-width:var(--maxw);margin:0 auto;padding:12px 24px;
  display:flex;align-items:center;gap:14px;}
.brand{display:flex;align-items:center;gap:10px;font-weight:800;font-size:19px;color:var(--text);}
.brand .logo{width:34px;height:34px;flex:0 0 auto;}
.brand em{font-style:normal;color:var(--accent);}
.nav-links{margin-left:auto;display:flex;gap:8px;align-items:center;}
.nav-links a{
  color:var(--text-secondary);font-weight:600;font-size:14.5px;
  padding:8px 14px;border-radius:999px;transition:.18s;
}
.nav-links a:hover{background:var(--brand-soft);color:var(--brand);}

/* ---------- 按钮 ---------- */
.btn{
  display:inline-flex;align-items:center;gap:8px;
  padding:12px 22px;border-radius:999px;font-weight:700;font-size:15px;
  border:1px solid transparent;cursor:pointer;transition:.18s;
  line-height:1;
}
.btn-primary{background:var(--brand);color:#fff;box-shadow:var(--shadow-sm);}
.btn-primary:hover{background:#234bb0;box-shadow:var(--shadow);transform:translateY(-1px);}
.btn-ghost{background:#fff;color:var(--brand);border-color:var(--line);}
.btn-ghost:hover{border-color:var(--brand);background:var(--brand-soft);}

/* ---------- Hero ---------- */
.hero{position:relative;overflow:hidden;padding:74px 0 56px;}
.hero-grid{display:grid;grid-template-columns:1.05fr .95fr;gap:40px;align-items:center;}
.hero h1{
  font-size:clamp(30px,5vw,52px);line-height:1.15;margin:0 0 18px;
  letter-spacing:.5px;
}
.hero h1 .hl{color:var(--brand);}
.hero h1 .dot{color:var(--accent);}
.hero p.lead{font-size:17px;color:var(--text-secondary);margin:0 0 28px;max-width:46ch;}
.hero-cta{display:flex;gap:14px;flex-wrap:wrap;}
.hero-art{position:relative;aspect-ratio:1/1;display:flex;align-items:center;justify-content:center;}
.hero-art svg{width:100%;height:100%;filter:drop-shadow(0 18px 40px rgba(43,89,195,0.18));}
.hero-badges{display:flex;gap:10px;margin-top:26px;flex-wrap:wrap;}
.badge{
  font-size:13px;font-weight:700;color:var(--brand);
  background:var(--brand-soft);border:1px solid var(--line-soft);
  padding:6px 13px;border-radius:999px;
}

/* ---------- 自学方法 3 步 ---------- */
.steps{display:grid;grid-template-columns:repeat(3,1fr);gap:20px;}
.step{
  background:var(--card);border:1px solid var(--line);border-radius:var(--radius);
  padding:24px;box-shadow:var(--shadow-sm);transition:.2s;
}
.step:hover{box-shadow:var(--shadow);transform:translateY(-3px);}
.step .num{
  width:38px;height:38px;border-radius:11px;display:grid;place-items:center;
  font-weight:800;color:#fff;background:var(--brand);margin-bottom:14px;font-size:17px;
}
.step h3{margin:0 0 8px;font-size:18px;}
.step p{margin:0;color:var(--muted);font-size:14.5px;}

/* ---------- 课程卡片 ---------- */
.cards{display:grid;grid-template-columns:repeat(auto-fill,minmax(320px,1fr));gap:22px;}
.course-card{
  background:var(--card);border:1px solid var(--line);border-radius:var(--radius);
  padding:0;overflow:hidden;box-shadow:var(--shadow-sm);transition:.22s;display:flex;flex-direction:column;
}
.course-card:hover{box-shadow:var(--shadow-lg);transform:translateY(-4px);}
.course-card .thumb{height:150px;position:relative;overflow:hidden;
  background:linear-gradient(135deg,var(--brand),var(--brand-2));}
.course-card .thumb svg{position:absolute;inset:0;width:100%;height:100%;opacity:.9;}
.course-card .tag{
  position:absolute;top:12px;left:12px;font-size:12px;font-weight:700;color:#fff;
  background:rgba(0,0,0,0.25);padding:4px 11px;border-radius:999px;backdrop-filter:blur(4px);
}
.course-card .body{padding:18px 20px 20px;display:flex;flex-direction:column;gap:10px;flex:1;}
.course-card h3{margin:0;font-size:19px;}
.course-card .meta{font-size:13.5px;color:var(--muted);margin:0;}
.course-card .desc{font-size:14px;color:var(--text-secondary);margin:0;flex:1;}
.course-card .foot{display:flex;align-items:center;justify-content:space-between;margin-top:6px;}
.pill{
  display:inline-flex;align-items:center;gap:7px;font-size:12.5px;font-weight:700;
  padding:5px 12px;border-radius:999px;background:var(--card-elevated);color:var(--text-secondary);
  border:1px solid var(--line);
}
.pill .d{width:8px;height:8px;border-radius:50%;background:var(--ok);}
.pill.live .d{background:var(--ok);}
.pill.soon .d{background:var(--warn);}

/* ---------- 课程地图（知识点） ---------- */
.map-grade{margin-bottom:34px;}
.map-grade .ghead{display:flex;align-items:center;gap:12px;margin-bottom:14px;}
.map-grade .ghead .g{font-weight:800;font-size:16px;color:#fff;background:var(--brand);
  padding:5px 14px;border-radius:999px;}
.map-grade .ghead .line{flex:1;height:1px;background:var(--line);}
.topics{display:flex;flex-wrap:wrap;gap:10px;}
.topic{
  font-size:14px;font-weight:600;color:var(--text-secondary);
  background:var(--card);border:1px solid var(--line);border-radius:10px;
  padding:9px 15px;transition:.16s;
}
.topic:hover{border-color:var(--brand);color:var(--brand);background:var(--brand-soft);transform:translateY(-2px);}
.topic.done{border-color:var(--brand-2-soft);background:var(--brand-2-soft);color:var(--brand-2);}
.topic.done::after{content:" ✓";color:var(--ok);font-weight:800;}

/* ---------- 页脚 ---------- */
.footer{margin-top:80px;background:var(--panel);border-top:1px solid var(--line);}
.footer-inner{max-width:var(--maxw);margin:0 auto;padding:40px 24px;
  display:flex;justify-content:space-between;gap:24px;flex-wrap:wrap;align-items:center;}
.footer .brand{font-size:18px;}
.footer p{color:var(--muted);font-size:13.5px;margin:6px 0 0;}

/* ---------- 入场动效 ---------- */
@keyframes xtFadeUp{from{opacity:0;transform:translateY(16px);}to{opacity:1;transform:none;}}
.reveal{animation:xtFadeUp .6s cubic-bezier(.2,.7,.3,1) both;}
.reveal.d1{animation-delay:.08s;}
.reveal.d2{animation-delay:.16s;}
.reveal.d3{animation-delay:.24s;}
@media (prefers-reduced-motion:reduce){
  *{animation:none!important;scroll-behavior:auto!important;}
  .reveal{opacity:1!important;transform:none!important;}
}

/* ---------- 响应式 ---------- */
@media (max-width:880px){
  .hero-grid{grid-template-columns:1fr;}
  .hero-art{max-width:340px;margin:0 auto;}
  .steps{grid-template-columns:1fr;}
  .nav-links{display:none;}
}