:root{
  --primary:#2f6fed;--primary-d:#1d54c4;--bg:#f4f6fb;--card:#fff;
  --text:#222;--muted:#888;--line:#eee;--radius:12px;
}
*{box-sizing:border-box;-webkit-tap-highlight-color:transparent}
body{margin:0;font-family:-apple-system,BlinkMacSystemFont,"Segoe UI",Roboto,"PingFang SC","Microsoft YaHei",sans-serif;background:var(--bg);color:var(--text);font-size:15px;line-height:1.6}
a{color:inherit;text-decoration:none}
img{max-width:100%;display:block}
.container{max-width:1100px;margin:0 auto;padding:0 14px}
.card{background:var(--card);border-radius:var(--radius);box-shadow:0 2px 12px rgba(0,0,0,.04)}
.btn{display:inline-block;background:var(--primary);color:#fff;padding:10px 18px;border-radius:8px;border:0;cursor:pointer;font-size:15px}
.btn:active{background:var(--primary-d)}
.btn-ghost{background:#fff;color:var(--primary);border:1px solid var(--primary)}
.input{width:100%;padding:11px 12px;border:1px solid #ddd;border-radius:8px;font-size:15px;margin:6px 0}
.tag{display:inline-block;font-size:12px;padding:2px 8px;border-radius:20px;background:#eef3ff;color:var(--primary)}
.price{color:#f5222d;font-weight:700}
.muted{color:var(--muted);font-size:13px}

/* 顶部导航 */
.topbar{background:#fff;border-bottom:1px solid var(--line);position:sticky;top:0;z-index:20}
.topbar .container{display:flex;align-items:center;height:54px;gap:14px}
.logo{font-weight:800;font-size:18px;color:var(--primary)}
.search{flex:1;display:flex;background:#f1f3f7;border-radius:20px;padding:6px 14px}
.search input{border:0;background:transparent;flex:1;outline:none}
.navlink{font-size:14px;color:#555}

/* 首页轮播/板块 */
.hero{margin:14px 0;border-radius:var(--radius);overflow:hidden}
.hero img{width:100%;height:180px;object-fit:cover}
.section{margin:18px 0}
.section h2{font-size:17px;margin:0 0 12px;display:flex;justify-content:space-between;align-items:center}
.section h2 a{font-size:13px;color:var(--muted);font-weight:400}

/* 课程网格 */
.grid{display:grid;grid-template-columns:repeat(2,1fr);gap:12px}
@media(min-width:768px){.grid{grid-template-columns:repeat(4,1fr)}}
.course{background:var(--card);border-radius:var(--radius);overflow:hidden;box-shadow:0 2px 12px rgba(0,0,0,.04)}
.course .cover{aspect-ratio:16/10;object-fit:cover;width:100%}
.course .body{padding:10px}
.course .title{font-size:14px;line-height:1.4;height:39px;overflow:hidden}
.course .meta{display:flex;justify-content:space-between;align-items:center;margin-top:6px}

/* 课程详情 */
.detail-cover{width:100%;border-radius:var(--radius)}
.chapter{background:#fff;border-radius:10px;padding:12px 14px;margin:8px 0;display:flex;justify-content:space-between;align-items:center}
.vip-free{background:#fff7e6;color:#d48806;font-size:12px;padding:2px 8px;border-radius:6px}

/* 底部导航(手机) */
.tabbar{position:fixed;bottom:0;left:0;right:0;background:#fff;border-top:1px solid var(--line);display:flex;z-index:30}
.tabbar a{flex:1;text-align:center;padding:8px 0;font-size:12px;color:#666}
.tabbar a.active{color:var(--primary)}
@media(min-width:768px){.tabbar{display:none}}

/* 通用列表 */
.list{background:#fff;border-radius:var(--radius);overflow:hidden}
.list .item{padding:14px;border-bottom:1px solid var(--line);display:flex;justify-content:space-between;gap:12px}
.empty{padding:40px;text-align:center;color:var(--muted)}

/* 表单页 */
.auth{max-width:400px;margin:8vh auto;padding:0 14px}
.auth .card{padding:24px}
.auth h1{font-size:20px;margin:0 0 16px;text-align:center}
.msg-box{margin:30px auto;max-width:420px;text-align:center;padding:30px}
.msg-box .btn{margin-top:16px}