/* ===== 研途课堂 · 简约有质感主题 ===== */
:root{
  --bg:#f6f7f9;
  --card:#ffffff;
  --ink:#1c2430;
  --muted:#7a8494;
  --line:#e8ebf0;
  --brand:#2f5aef;
  --brand-dark:#2347c4;
  --brand-soft:#eef3ff;
  --radius:14px;
  --shadow:0 2px 12px rgba(28,36,48,.06);
  --shadow-lg:0 12px 40px rgba(28,36,48,.12);
}
*{box-sizing:border-box;margin:0;padding:0}
body{
  font-family:-apple-system,BlinkMacSystemFont,"PingFang SC","Microsoft YaHei",sans-serif;
  background:var(--bg);color:var(--ink);
  -webkit-font-smoothing:antialiased;line-height:1.6;
}

/* ===== 登录页 ===== */
.login-wrap{min-height:100vh;display:flex;align-items:center;justify-content:center;padding:20px;
  background:linear-gradient(160deg,#eef3ff 0%,#f6f7f9 45%);}
.login-card{background:var(--card);width:100%;max-width:400px;padding:44px 36px 32px;
  border-radius:20px;box-shadow:var(--shadow-lg);}
.brand{text-align:center;margin-bottom:28px}
.brand-mark{width:56px;height:56px;margin:0 auto 14px;border-radius:16px;
  background:linear-gradient(145deg,var(--brand),#5b7dff);color:#fff;
  font-size:26px;font-weight:700;display:flex;align-items:center;justify-content:center;
  box-shadow:0 8px 20px rgba(47,90,239,.32);}
.brand h1{font-size:22px;letter-spacing:1px}
.brand-sub{color:var(--muted);font-size:13px;margin-top:6px}
#loginForm label{display:block;font-size:13px;color:var(--muted);margin:16px 0 6px}
#loginForm input{width:100%;padding:13px 14px;border:1px solid var(--line);border-radius:10px;
  font-size:15px;transition:border .2s,box-shadow .2s;background:#fbfcfe}
#loginForm input:focus{outline:none;border-color:var(--brand);box-shadow:0 0 0 3px var(--brand-soft);background:#fff}
.login-err{color:#e23b3b;font-size:13px;min-height:20px;margin-top:10px}
.btn-primary{width:100%;margin-top:10px;padding:14px;border:none;border-radius:11px;
  background:var(--brand);color:#fff;font-size:16px;font-weight:600;cursor:pointer;
  transition:background .2s,transform .1s;letter-spacing:4px}
.btn-primary:hover{background:var(--brand-dark)}
.btn-primary:active{transform:scale(.98)}
.login-hint{margin-top:22px;padding:12px 14px;background:#f4f6fa;border-radius:10px;
  font-size:12.5px;color:var(--muted);text-align:center;line-height:1.9}
.login-hint code{background:#e7ebf3;padding:1px 6px;border-radius:5px;color:var(--ink);font-size:12px}

/* ===== 主框架 ===== */
.topbar{background:var(--card);border-bottom:1px solid var(--line);
  display:flex;align-items:center;justify-content:space-between;padding:0 28px;height:62px;
  position:sticky;top:0;z-index:10}
.topbar-brand{font-weight:700;font-size:18px;letter-spacing:1px}
.topbar-right{display:flex;align-items:center;gap:14px}
.user-label{color:var(--muted);font-size:14px}
.btn-ghost{background:none;border:1px solid var(--line);padding:7px 16px;border-radius:9px;
  font-size:13px;color:var(--ink);cursor:pointer;transition:.2s}
.btn-ghost:hover{border-color:var(--brand);color:var(--brand)}
.container{max-width:960px;margin:0 auto;padding:32px 24px 60px}
.page-title{font-size:22px;margin-bottom:22px}

/* ===== 课程卡片 ===== */
.course-grid{display:grid;grid-template-columns:repeat(auto-fill,minmax(260px,1fr));gap:20px}
.course-card{background:var(--card);border-radius:var(--radius);padding:24px;cursor:pointer;
  box-shadow:var(--shadow);transition:transform .2s,box-shadow .2s;border:1px solid transparent}
.course-card:hover{transform:translateY(-4px);box-shadow:var(--shadow-lg);border-color:var(--brand-soft)}
.course-cover{width:52px;height:52px;border-radius:13px;background:var(--brand-soft);
  display:flex;align-items:center;justify-content:center;font-size:26px;margin-bottom:16px}
.course-card h3{font-size:17px;margin-bottom:8px}
.course-card p{color:var(--muted);font-size:13.5px}
.course-card .go{margin-top:16px;color:var(--brand);font-size:13px;font-weight:600}
.empty{color:var(--muted);text-align:center;padding:60px 0;font-size:14px}

/* ===== 课程详情 ===== */
.btn-back{background:none;border:none;color:var(--brand);font-size:14px;cursor:pointer;
  padding:6px 0;margin-bottom:18px;font-weight:600}
.btn-back:hover{text-decoration:underline}
.course-head{display:flex;gap:20px;background:var(--card);padding:24px;border-radius:var(--radius);
  box-shadow:var(--shadow);margin-bottom:24px;align-items:center}
.course-cover-lg{width:64px;height:64px;border-radius:16px;background:var(--brand-soft);
  display:flex;align-items:center;justify-content:center;font-size:32px;flex-shrink:0}
.course-head h2{font-size:20px;margin-bottom:6px}
.course-head .muted{color:var(--muted);font-size:14px}
.lesson-count{color:var(--brand);font-size:13px;margin-top:8px;font-weight:600}
.lesson-list{background:var(--card);border-radius:var(--radius);box-shadow:var(--shadow);overflow:hidden}
.chapter-header{padding:12px 22px;background:#f0f3f8;color:var(--brand);font-size:14px;font-weight:700;
  border-bottom:1px solid var(--line);letter-spacing:.5px}
.lesson-item{display:flex;align-items:center;gap:16px;padding:16px 22px;border-bottom:1px solid var(--line);
  cursor:pointer;transition:background .15s}
.lesson-item:last-child{border-bottom:none}
.lesson-item:hover{background:var(--brand-soft)}
.lesson-no{width:34px;height:34px;border-radius:9px;background:#f0f3f8;color:var(--muted);
  display:flex;align-items:center;justify-content:center;font-size:13px;font-weight:600;flex-shrink:0}
.lesson-item:hover .lesson-no{background:var(--brand);color:#fff}
.lesson-title{flex:1;font-size:15px}
.lesson-dur{color:var(--muted);font-size:13px}
.lesson-play{color:var(--brand);font-size:13px;font-weight:600}

/* ===== 播放器 ===== */
.player-title{font-size:19px;margin:6px 0 18px}
.player-box{background:#000;border-radius:var(--radius);overflow:hidden;box-shadow:var(--shadow-lg)}
.player-box video{width:100%;display:block;aspect-ratio:16/9;background:#000}
.speed-bar{display:flex;align-items:center;gap:10px;margin-top:18px;color:var(--muted);font-size:14px}
.speed-bar button{background:var(--card);border:1px solid var(--line);border-radius:8px;
  padding:7px 16px;cursor:pointer;font-size:13px;transition:.15s}
.speed-bar button:hover{border-color:var(--brand);color:var(--brand)}

/* ===== 右侧悬浮按钮 ===== */
.float-nav{position:fixed;right:22px;bottom:80px;z-index:99;display:flex;flex-direction:column;gap:12px}
.float-btn{width:48px;height:48px;border-radius:50%;border:none;cursor:pointer;
  background:var(--brand);color:#fff;font-size:20px;font-weight:700;
  box-shadow:0 4px 16px rgba(47,90,239,.4);transition:.2s}
.float-btn:hover{background:var(--brand-dark);transform:translateY(-2px)}
#btnTop{transition:opacity .3s}

@media(max-width:600px){
  .container{padding:20px 16px 50px}
  .course-head{flex-direction:column;align-items:flex-start}
}