:root{
  --bg:#eef2f9; --panel:#ffffff; --panel-2:#f6f8fc; --ink:#1e293b; --muted:#64748b;
  --line:#e2e8f0; --primary:#2563eb; --primary-d:#1e40af; --primary-soft:#eff4ff;
  --amber:#f59e0b; --green:#16a34a; --red:#dc2626; --radius:14px; --shadow:0 6px 22px rgba(30,58,138,.07);
}
[data-theme="dark"]{
  --bg:#0f172a; --panel:#1e293b; --panel-2:#172033; --ink:#e2e8f0; --muted:#94a3b8;
  --line:#334155; --primary:#60a5fa; --primary-d:#3b82f6; --primary-soft:#1e3a5f;
  --amber:#fbbf24; --green:#4ade80; --red:#f87171; --shadow:0 6px 22px rgba(0,0,0,.3);
}
*{box-sizing:border-box}
html,body{margin:0;height:100%}
body{font-family:-apple-system,"PingFang SC","Microsoft YaHei",sans-serif;background:var(--bg);color:var(--ink)}
.hidden{display:none!important}
button{font-family:inherit;cursor:pointer}
.muted{color:var(--muted)} .small{font-size:12px}

/* 布局 */
.layout{display:flex;height:100vh}
.sidebar{width:230px;background:var(--panel);border-right:1px solid var(--line);display:flex;flex-direction:column;padding:18px 14px}
.brand{display:flex;gap:10px;align-items:center;margin-bottom:22px}
.brand-logo{width:42px;height:42px;border-radius:12px;background:linear-gradient(135deg,var(--primary),var(--primary-d));color:#fff;display:flex;align-items:center;justify-content:center;font-size:22px;font-weight:700}
.brand-text{font-size:14px;font-weight:700;line-height:1.2}
.brand-text span{font-size:11px;color:var(--muted);font-weight:500}
.nav{display:flex;flex-direction:column;gap:4px;flex:1}
.nav-item{display:flex;align-items:center;gap:10px;text-align:left;background:none;border:none;padding:11px 12px;border-radius:10px;color:var(--ink);font-size:14px;font-weight:500}
.nav-item:hover{background:var(--panel-2)}
.nav-item.active{background:var(--primary-soft);color:var(--primary-d);font-weight:700}
.ni{font-size:17px;width:20px;text-align:center}
.side-foot{border-top:1px solid var(--line);padding-top:12px;display:flex;align-items:center;justify-content:space-between}
.user-chip{display:flex;align-items:center;gap:8px}
.avatar{width:30px;height:30px;border-radius:50%;background:var(--primary);color:#fff;display:flex;align-items:center;justify-content:center;font-size:13px;font-weight:700}
.uname{font-size:13px}
.link-btn{background:none;border:none;color:var(--muted);font-size:12px;text-decoration:underline}

.main{flex:1;display:flex;flex-direction:column;min-width:0}
.topbar{height:60px;display:flex;align-items:center;justify-content:space-between;padding:0 26px;border-bottom:1px solid var(--line);background:var(--panel)}
.topbar h1{font-size:18px;margin:0}
.top-actions{display:flex;gap:8px}
.icon-btn{width:38px;height:38px;border-radius:10px;border:1px solid var(--line);background:var(--panel);font-size:17px}
.content{flex:1;overflow:auto;padding:24px 26px}
.view{min-height:100%}

/* 按钮 */
.btn{border:none;border-radius:10px;padding:10px 16px;font-size:14px;font-weight:600}
.btn-primary{background:var(--primary);color:#fff}
.btn-primary:hover{background:var(--primary-d)}
.btn-outline{background:none;border:1px solid var(--line);color:var(--ink)}
.btn-amber{background:var(--amber);color:#3a2a00}
.btn-block{width:100%;margin-top:8px;padding:12px}
.btn-sm{padding:6px 12px;font-size:13px}

/* 课程内容 */
.course-layout{display:grid;grid-template-columns:220px 1fr;gap:20px}
.course-menu{background:var(--panel);border:1px solid var(--line);border-radius:var(--radius);padding:12px;height:fit-content;position:sticky;top:0}
.cm-module{font-weight:700;font-size:13px;color:var(--primary-d);margin:10px 6px 4px}
.cm-sec{padding:8px 10px;border-radius:8px;font-size:13px;color:var(--ink);cursor:pointer}
.cm-sec:hover{background:var(--panel-2)}
.cm-sec.active{background:var(--primary-soft);color:var(--primary-d);font-weight:700}
.course-panel{background:var(--panel);border:1px solid var(--line);border-radius:var(--radius);padding:22px;min-height:400px}
.cp-title{font-size:20px;font-weight:700;margin:0 0 4px}
.cp-desc{color:var(--muted);font-size:13px;margin-bottom:18px}
.slide{border:1px solid var(--line);border-radius:12px;padding:18px;margin-bottom:14px;background:var(--panel-2)}
.slide h3{margin:0 0 8px;font-size:16px}
.slide p{margin:0;line-height:1.8;font-size:14px;white-space:pre-wrap}
.slide img{max-width:100%;border-radius:8px;margin-top:10px}
.slide-imgs{display:flex;flex-direction:column;gap:10px;margin-top:10px}
.slide-imgs img{max-width:100%;border-radius:8px;border:1px solid var(--line)}
.slide-imgonly{padding:14px}
.slide-imgonly h3{font-size:13px;color:var(--muted);font-weight:600;margin-bottom:10px}

/* 聊天 */
.chat-wrap{display:flex;flex-direction:column;height:calc(100vh - 150px)}
.chat-box{flex:1;overflow:auto;display:flex;flex-direction:column;gap:14px;padding-right:6px}
.bubble{max-width:78%;padding:12px 15px;border-radius:14px;font-size:14px;line-height:1.75;white-space:pre-wrap}
.bubble.user{align-self:flex-end;background:var(--primary);color:#fff;border-bottom-right-radius:4px}
.bubble.ai{align-self:flex-start;background:var(--panel);border:1px solid var(--line);border-bottom-left-radius:4px}
.chat-input{display:flex;gap:10px;margin-top:12px}
.chat-input textarea{flex:1;resize:none;height:52px;border:1px solid var(--line);border-radius:12px;padding:12px;font-family:inherit;font-size:14px;background:var(--panel);color:var(--ink)}

/* 练习 */
.subtabs{display:flex;gap:8px;margin-bottom:18px;flex-wrap:wrap}
.subtab{padding:8px 16px;border-radius:20px;border:1px solid var(--line);background:var(--panel);font-size:13px;font-weight:600;color:var(--muted)}
.subtab.active{background:var(--primary);color:#fff;border-color:var(--primary)}
.ex-card{background:var(--panel);border:1px solid var(--line);border-radius:var(--radius);padding:20px;margin-bottom:16px}
.ex-meta{display:flex;gap:8px;margin-bottom:10px;flex-wrap:wrap}
.tag{font-size:12px;padding:3px 10px;border-radius:20px;background:var(--primary-soft);color:var(--primary-d);font-weight:600}
.tag.amber{background:#fef3c7;color:#92400e}
.ex-q{font-size:15px;line-height:1.8;white-space:pre-wrap;margin-bottom:12px}
.ex-textarea{width:100%;min-height:120px;border:1px solid var(--line);border-radius:10px;padding:12px;font-family:inherit;font-size:14px;background:var(--panel-2);color:var(--ink)}
.opt-row{display:flex;gap:10px;align-items:center;padding:10px 14px;border:1px solid var(--line);border-radius:10px;margin-bottom:8px;cursor:pointer}
.opt-row.sel{border-color:var(--primary);background:var(--primary-soft)}
.opt-lbl{width:26px;height:26px;border-radius:50%;background:var(--panel-2);display:flex;align-items:center;justify-content:center;font-weight:700;font-size:13px}
.ex-answer{margin-top:12px;padding:12px 14px;border-radius:10px;background:var(--panel-2);font-size:13px;line-height:1.7}
.ex-answer.ok{border-left:3px solid var(--green)}
.ex-answer .lbl{font-weight:700;color:var(--primary-d)}

/* 卡片 */
.filter-row{display:flex;gap:8px;margin-bottom:16px;flex-wrap:wrap}
.card-grid{display:grid;grid-template-columns:repeat(auto-fill,minmax(240px,1fr));gap:16px}
.flip-card{background:var(--panel);border:1px solid var(--line);border-radius:var(--radius);padding:18px;min-height:150px;display:flex;flex-direction:column;cursor:pointer;transition:transform .15s}
.flip-card:hover{transform:translateY(-3px);box-shadow:var(--shadow)}
.fc-cat{font-size:11px;font-weight:700;color:var(--amber);margin-bottom:8px}
.fc-title{font-size:16px;font-weight:700;margin-bottom:8px}
.fc-body{font-size:13px;line-height:1.7;color:var(--ink);flex:1}
.fc-dur{font-size:11px;color:var(--muted);margin-top:10px}

/* 理念 */
.idea-grid{display:grid;grid-template-columns:repeat(auto-fill,minmax(260px,1fr));gap:18px}
.idea-card{background:linear-gradient(135deg,var(--primary-soft),var(--panel));border:1px solid var(--line);border-radius:var(--radius);padding:24px}
.idea-emoji{font-size:34px}
.idea-card h3{margin:12px 0 8px;font-size:18px}
.idea-card p{margin:0;line-height:1.8;font-size:14px;color:var(--muted)}

/* 弹窗 */
.modal-mask{position:fixed;inset:0;background:rgba(15,23,42,.5);display:flex;align-items:center;justify-content:center;z-index:50}
.modal{background:var(--panel);border-radius:18px;padding:28px;width:340px;box-shadow:var(--shadow)}
.login-card h2{margin:0 0 4px;font-size:20px}
.login-card label{display:block;font-size:13px;font-weight:600;margin:14px 0 6px}
.login-card input{width:100%;padding:11px 12px;border:1px solid var(--line);border-radius:10px;font-size:14px;background:var(--panel-2);color:var(--ink)}

/* toast */
.toast{position:fixed;bottom:30px;left:50%;transform:translateX(-50%);background:var(--ink);color:#fff;padding:10px 18px;border-radius:24px;font-size:13px;opacity:0;transition:opacity .25s;pointer-events:none;z-index:60}
.toast.show{opacity:1}

/* 优秀作业 */
.show-grid{display:grid;grid-template-columns:repeat(auto-fill,minmax(280px,1fr));gap:16px}
.show-card{background:var(--panel);border:1px solid var(--line);border-radius:var(--radius);overflow:hidden}
.show-card .sc-body{padding:16px}
.show-card h4{margin:0 0 6px;font-size:15px}
.show-card .sc-meta{font-size:12px;color:var(--muted);margin-bottom:8px}
.show-card video,.show-card iframe{width:100%;aspect-ratio:16/9;background:#000;display:block}
.show-card .sc-text{font-size:13px;line-height:1.7;color:var(--ink);max-height:90px;overflow:auto;margin-top:8px}
.sc-play{display:inline-block;margin-top:8px;color:var(--primary-d);font-size:13px;font-weight:600}
.sc-link-btn{display:inline-block;margin-top:8px;padding:9px 16px;background:var(--primary);color:#fff;border-radius:9px;text-decoration:none;font-size:14px;font-weight:600}
.sc-link-btn:hover{opacity:.9}

@media(max-width:720px){
  .layout{flex-direction:column}
  .sidebar{width:100%;flex-direction:row;overflow:auto;padding:10px}
  .nav{flex-direction:row;flex:1}
  .side-foot{display:none}
  .course-layout{grid-template-columns:1fr}
}