/* ===== Reset & Base ===== */
*,*::before,*::after{box-sizing:border-box;margin:0;padding:0}
:root{
  --bg:#f8f9fc;--bg2:#fff;--text:#1a1a2e;--text2:#555;--accent:#4361ee;--accent2:#3a0ca3;
  --hot:#ff006e;--warm:#fb5607;--green:#06d6a0;--border:#e2e6ef;
  --sidebar-bg:#1a1a2e;--sidebar-text:#c8c8d8;--sidebar-active:#fff;
  --radius:10px;--shadow:0 2px 12px rgba(0,0,0,.06);
  --font:-apple-system,BlinkMacSystemFont,"Segoe UI","Noto Sans SC",sans-serif;
  --mono:"JetBrains Mono","Fira Code","Cascadia Code",monospace;
}
html{scroll-behavior:smooth;font-size:15px}
body{font-family:var(--font);color:var(--text);background:var(--bg);display:flex;min-height:100vh;line-height:1.7}

/* ===== Sidebar ===== */
.sidebar{
  position:fixed;top:0;left:0;width:260px;height:100vh;background:var(--sidebar-bg);
  color:var(--sidebar-text);display:flex;flex-direction:column;z-index:100;
  overflow-y:auto;scrollbar-width:thin;
}
.sidebar::-webkit-scrollbar{width:6px}
.sidebar::-webkit-scrollbar-thumb{background:rgba(255,255,255,.1);border-radius:3px}
.brand{display:flex;align-items:center;gap:12px;padding:24px 20px 16px}
.logo{width:40px;height:40px;border-radius:10px;background:var(--accent);color:#fff;display:flex;align-items:center;justify-content:center;font-weight:700;font-size:18px}
.brand h1{font-size:16px;color:#fff;font-weight:600}
.brand p,.brand-sub{font-size:11px;opacity:.6}

/* ===== 期中/期末 视图切换标签 ===== */
.view-switch{display:flex;gap:6px;padding:0 16px 12px;margin-top:-4px}
.view-tab{flex:1;padding:8px 6px;border:1px solid rgba(255,255,255,.14);background:rgba(255,255,255,.04);
  color:var(--sidebar-text);border-radius:8px;cursor:pointer;font-size:12.5px;font-weight:600;
  font-family:inherit;transition:.15s}
.view-tab:hover{background:rgba(255,255,255,.1);color:#fff}
.view-tab.active{background:var(--accent);border-color:var(--accent);color:#fff}
.view[hidden],nav[hidden]{display:none}

nav{flex:1;padding:0 12px}
.nav-section{margin-bottom:8px}
.nav-title{display:block;font-size:10px;text-transform:uppercase;letter-spacing:1.5px;color:rgba(255,255,255,.3);padding:12px 8px 4px;font-weight:600}
.nav-item{display:block;padding:6px 12px;border-radius:6px;color:var(--sidebar-text);text-decoration:none;font-size:13px;transition:.15s}
.nav-item:hover{background:rgba(255,255,255,.08);color:#fff}
.nav-item.active{background:var(--accent);color:#fff;font-weight:500}
.progress{padding:16px 20px 24px}
.progress-label{font-size:11px;display:flex;justify-content:space-between;margin-bottom:6px;opacity:.6}
.progress-bar{height:4px;background:rgba(255,255,255,.1);border-radius:4px;overflow:hidden}
.progress-fill{height:100%;width:0;background:var(--green);border-radius:4px;transition:width .4s}

/* ===== Content ===== */
.content{margin-left:260px;flex:1;min-width:0}
.container{max-width:860px;margin:0 auto;padding:40px 48px 80px}

/* ===== Hero ===== */
.hero{background:linear-gradient(135deg,var(--accent),var(--accent2));color:#fff;border-radius:16px;padding:48px 40px;margin-bottom:40px}
.hero-tag{display:inline-block;background:rgba(255,255,255,.15);padding:4px 14px;border-radius:20px;font-size:12px;margin-bottom:16px}
.hero-title{font-size:2.4rem;font-weight:800;line-height:1.2;margin-bottom:12px}
.hero-sub{font-size:15px;opacity:.85;max-width:520px;line-height:1.6}
.hero-stats{display:flex;gap:32px;margin-top:28px;flex-wrap:wrap}
.stat{text-align:center}
.stat b{display:block;font-size:28px;font-weight:800}
.stat span{font-size:12px;opacity:.7}

/* ===== Headings ===== */
.chapter{padding-top:20px;margin-bottom:60px;scroll-margin-top:20px}
.chapter h1{font-size:1.6rem;font-weight:700;margin-bottom:24px;padding-bottom:12px;border-bottom:2px solid var(--border)}
.chapter h2{font-size:1.15rem;font-weight:600;margin:28px 0 12px;color:var(--accent2)}
.chapter h3{font-size:1rem;font-weight:600;margin:16px 0 8px}
.chapter p{margin:8px 0}

/* ===== Code ===== */
code{font-family:var(--mono);background:#eef0fa;padding:1px 6px;border-radius:4px;font-size:.9em;color:var(--accent2)}
pre{background:#1a1a2e;color:#e8e8f0;padding:14px 18px;border-radius:var(--radius);overflow-x:auto;font-family:var(--mono);font-size:13px;line-height:1.6;margin:12px 0}
pre code{background:none;padding:0;color:inherit}

/* ===== Tables ===== */
.tbl{width:100%;border-collapse:collapse;margin:12px 0 20px;font-size:14px}
.tbl th{background:var(--accent);color:#fff;padding:10px 14px;text-align:left;font-weight:500}
.tbl td{padding:9px 14px;border-bottom:1px solid var(--border);vertical-align:top}
.tbl tr:hover td{background:#f0f2ff}

/* ===== Callouts ===== */
.callout{border-radius:var(--radius);padding:16px 20px;margin:16px 0;font-size:14px;line-height:1.7}
.callout.tip{background:#e8f5e9;border-left:4px solid var(--green)}
.callout.warn{background:#fff3e0;border-left:4px solid var(--warm)}
.callout.important{background:#e8eaf6;border-left:4px solid var(--accent)}
.warn-text{color:var(--warm);font-size:14px}
.source-tag{display:inline-block;margin-left:8px;padding:2px 8px;border-radius:999px;font-size:11px;font-weight:700;vertical-align:middle}
.source-tag.non-courseware{background:#fff3e0;color:var(--warm);border:1px solid rgba(251,86,7,.2)}

/* ===== Knowledge Points ===== */
.kp-list{list-style:none;padding:0}
.kp-list li{position:relative;padding:6px 0 6px 20px;font-size:14px}
.kp-list li::before{content:"";position:absolute;left:0;top:14px;width:8px;height:8px;border-radius:50%;background:var(--accent);opacity:.5}

/* ===== Inline MCQ (内嵌选择题，作答后才显示答案) ===== */
.mcq{background:var(--bg2);border:1.5px solid var(--border);border-radius:var(--radius);margin:14px 0;box-shadow:var(--shadow);padding:16px 22px}
.mcq .mcq-head{display:flex;align-items:flex-start;gap:10px;margin-bottom:10px;flex-wrap:wrap}
.mcq .mcq-stem{font-size:14.5px;font-weight:500;flex:1;min-width:0;line-height:1.7}
.mcq .mcq-mode-badge{display:inline-block;padding:3px 10px;border-radius:999px;background:#eef0fa;color:var(--accent2);font-size:11px;font-weight:700}
.mcq .mcq-opts{display:flex;flex-direction:column;gap:8px;margin:10px 0}
.mcq .mcq-opt{display:flex;gap:10px;padding:9px 14px;border:1.5px solid var(--border);border-radius:8px;cursor:pointer;font-size:14px;transition:.15s;align-items:flex-start;line-height:1.6}
.mcq .mcq-opt:hover{border-color:var(--accent);background:#f5f6ff}
.mcq .mcq-opt input{margin-top:5px;accent-color:var(--accent);flex-shrink:0}
.mcq .mcq-opt.selected{border-color:var(--accent);background:#eef2ff}
.mcq .mcq-opt.pending{box-shadow:inset 0 0 0 1px rgba(67,97,238,.15)}
.mcq .mcq-opt .opt-label{font-weight:600;color:var(--accent);margin-right:4px;flex-shrink:0}
.mcq.answered .mcq-opt{cursor:default;pointer-events:none}
.mcq .mcq-opt.correct{background:#e8f8f1;border-color:var(--green);font-weight:500}
.mcq .mcq-opt.correct .opt-label{color:var(--green)}
.mcq .mcq-opt.wrong{background:#fff0f0;border-color:var(--hot)}
.mcq .mcq-opt.wrong .opt-label{color:var(--hot)}
.mcq .mcq-opt.missed{background:#f0fdf4;border-color:var(--green)}
.mcq .mcq-explain{display:none;margin-top:12px;padding:12px 16px;background:#f0fdf4;border-left:3px solid var(--green);border-radius:6px;font-size:13.5px;line-height:1.75}
.mcq.answered .mcq-explain{display:block;animation:slideIn .25s ease}
.mcq .mcq-result-badge{display:none;padding:3px 12px;border-radius:12px;font-size:11px;font-weight:700;color:#fff;flex-shrink:0}
.mcq.answered.correct .mcq-result-badge{display:inline-block;background:var(--green)}
.mcq.answered.correct .mcq-result-badge::before{content:"✓ 正确"}
.mcq.answered.wrong .mcq-result-badge{display:inline-block;background:var(--hot)}
.mcq.answered.wrong .mcq-result-badge::before{content:"✗ 错误"}
.mcq.answered.revealed .mcq-result-badge{display:inline-block;background:var(--text2)}
.mcq.answered.revealed .mcq-result-badge::before{content:"已查看答案"}
.mcq .mcq-actions{margin-top:8px;display:flex;gap:8px}
.mcq .mcq-submit,
.mcq .mcq-reveal{padding:5px 14px;border:1.5px solid var(--accent);background:transparent;color:var(--accent);border-radius:6px;cursor:pointer;font-size:12px;font-weight:600;font-family:inherit;transition:.15s}
.mcq .mcq-submit{background:var(--accent);color:#fff}
.mcq .mcq-submit:hover{background:var(--accent2);border-color:var(--accent2)}
.mcq .mcq-reveal:hover{background:var(--accent);color:#fff}
.mcq.answered .mcq-reveal,.mcq.answered .mcq-submit{display:none}

@keyframes slideIn{from{opacity:0;transform:translateY(-4px)}to{opacity:1;transform:translateY(0)}}

/* ===== Open-ended question (非选择题，点击展开看答案) ===== */
.openq{background:var(--bg2);border:1.5px solid var(--border);border-radius:var(--radius);margin:14px 0;box-shadow:var(--shadow);padding:16px 22px}
.openq .openq-head{display:flex;align-items:flex-start;gap:10px;margin-bottom:8px;flex-wrap:wrap}
.openq .openq-stem{font-size:14.5px;font-weight:500;flex:1;min-width:0;line-height:1.7}
.openq .openq-toggle{padding:5px 14px;border:1.5px solid var(--accent);background:transparent;color:var(--accent);border-radius:6px;cursor:pointer;font-size:12px;font-weight:600;font-family:inherit;transition:.15s;flex-shrink:0}
.openq .openq-toggle:hover{background:var(--accent);color:#fff}
.openq.shown .openq-toggle{background:var(--text2);border-color:var(--text2);color:#fff}
.openq.shown .openq-toggle::after{content:" ↑"}
.openq .openq-answer{display:none;margin-top:12px;padding:14px 18px;background:#f0fdf4;border-left:3px solid var(--green);border-radius:6px;font-size:13.5px;line-height:1.75}
.openq.shown .openq-answer{display:block;animation:slideIn .25s ease}
.openq .openq-answer h4{color:var(--accent2);margin:10px 0 4px;font-size:14px}
.openq .openq-answer h4:first-child{margin-top:0}
.openq .openq-answer .step{background:#fff;border-left:3px solid var(--accent);padding:8px 12px;margin:8px 0;border-radius:4px}
.openq .openq-answer table{width:100%;border-collapse:collapse;margin:8px 0;font-size:13px}
.openq .openq-answer table th,.openq .openq-answer table td{border:1px solid var(--border);padding:5px 8px;text-align:left}
.openq .openq-answer table th{background:#eef0fa}
.openq .openq-answer pre{margin:10px 0}

/* ===== Big problem (题面外露 + 解答可展开) ===== */
.bigq{background:var(--bg2);border:1.5px solid var(--border);border-radius:var(--radius);margin:18px 0;box-shadow:var(--shadow);overflow:hidden}
.bigq-head{padding:14px 22px;background:linear-gradient(90deg,#fff,#f5f6ff);border-bottom:1px solid var(--border)}
.bigq-tag-row{display:flex;gap:8px;align-items:center;margin-bottom:6px;flex-wrap:wrap}
.bigq-title{font-size:15px;font-weight:600;color:var(--accent2)}
.bigq-stem{padding:14px 22px;font-size:14px;line-height:1.75;background:#fafbff}
.bigq-stem h4{color:var(--accent2);font-size:13px;margin:8px 0 4px}
.bigq-stem h4:first-child{margin-top:0}
.bigq-stem pre{margin:8px 0}
.bigq-actions{padding:10px 22px;border-top:1px dashed var(--border);background:#f5f6ff}
.bigq-toggle{padding:7px 18px;border:0;background:var(--accent);color:#fff;border-radius:6px;cursor:pointer;font-size:13px;font-weight:600;font-family:inherit;transition:.15s}
.bigq-toggle:hover{background:var(--accent2)}
.bigq.shown .bigq-toggle{background:var(--text2)}
.bigq.shown .bigq-toggle::after{content:" ↑ 收起"}
.bigq:not(.shown) .bigq-toggle::after{content:" → 查看解答"}
.bigq-solution{display:none;padding:16px 22px;background:#f0fdf4;border-top:1px dashed var(--green);font-size:13.5px;line-height:1.75}
.bigq.shown .bigq-solution{display:block;animation:slideIn .3s ease}
.bigq-solution h4{color:var(--accent2);margin:14px 0 6px;font-size:14px;padding-bottom:4px;border-bottom:1px dashed var(--border)}
.bigq-solution h4:first-child{margin-top:0}
.bigq-solution .step{background:#fff;border-left:3px solid var(--accent);padding:10px 14px;margin:10px 0;border-radius:4px}
.bigq-solution table{width:100%;border-collapse:collapse;margin:10px 0;font-size:13px}
.bigq-solution table th,.bigq-solution table td{border:1px solid var(--border);padding:5px 9px;text-align:left;vertical-align:top}
.bigq-solution table th{background:#eef0fa}
.bigq-solution pre{margin:10px 0}
.bigq-solution ul,.bigq-solution ol{padding-left:24px;margin:8px 0}
.bigq-solution ul li,.bigq-solution ol li{margin:4px 0}

/* ===== Quiz (legacy details, kept for compatibility) ===== */
.quiz{background:var(--bg2);border:1px solid var(--border);border-radius:var(--radius);margin:14px 0;box-shadow:var(--shadow);overflow:hidden}
.quiz summary{padding:14px 20px;cursor:pointer;font-size:14px;font-weight:500;list-style:none;display:flex;align-items:center;gap:10px;transition:.15s}
.quiz summary::-webkit-details-marker{display:none}
.quiz summary::before{content:"▶";font-size:10px;color:var(--accent);transition:transform .2s;flex-shrink:0}
.quiz[open] summary::before{transform:rotate(90deg)}
.quiz summary:hover{background:#f5f6ff}
.q-tag{display:inline-block;background:var(--accent);color:#fff;font-size:11px;padding:2px 10px;border-radius:12px;font-weight:600;flex-shrink:0}
.q-tag.big{background:var(--hot)}
.q-tag.solve{background:var(--green)}
.quiz ol,.quiz ul{padding:8px 20px 8px 48px;font-size:14px}
.quiz li{margin:4px 0}
.answer{background:#f0fdf4;border-top:1px dashed var(--green);padding:14px 20px;font-size:13.5px;line-height:1.75}
.answer h4{color:var(--accent2);margin:10px 0 4px;font-size:14px}
.answer .step{background:#fff;border-left:3px solid var(--accent);padding:8px 12px;margin:8px 0;border-radius:4px}
.answer table{width:100%;border-collapse:collapse;margin:8px 0;font-size:13px}
.answer table th,.answer table td{border:1px solid var(--border);padding:5px 8px;text-align:left}
.answer table th{background:#eef0fa}

/* ===== Weight Grid ===== */
.weight-grid{display:grid;grid-template-columns:repeat(2,1fr);gap:16px;margin:16px 0}
.weight-card{background:var(--bg2);border-radius:var(--radius);padding:20px;box-shadow:var(--shadow);border-top:3px solid var(--border)}
.weight-card.hot{border-top-color:var(--hot)}
.weight-card.warm{border-top-color:var(--warm)}
.weight-pct{font-size:28px;font-weight:800;color:var(--accent)}
.weight-card h3{margin:6px 0 4px;font-size:15px}
.weight-card p{font-size:13px;color:var(--text2)}

/* ===== Pipeline ===== */
.pipeline{display:flex;align-items:center;gap:8px;flex-wrap:wrap;margin:16px 0;font-size:14px;color:var(--text2)}
.pipe-box{background:var(--accent);color:#fff;padding:8px 16px;border-radius:8px;font-size:13px;font-weight:500}

/* ===== Roadmap ===== */
.roadmap{display:flex;flex-direction:column;gap:14px;margin:20px 0}
.road-step{display:flex;gap:16px;background:var(--bg2);padding:16px 20px;border-radius:var(--radius);box-shadow:var(--shadow);border-left:4px solid var(--accent)}
.road-num{width:36px;height:36px;border-radius:50%;background:var(--accent);color:#fff;display:flex;align-items:center;justify-content:center;font-weight:700;flex-shrink:0}
.road-step h3{font-size:15px;margin-bottom:2px}
.road-step p{font-size:13px;color:var(--text2)}

/* ===== Trap Grid ===== */
.trap-grid{display:grid;grid-template-columns:repeat(3,1fr);gap:12px;margin:16px 0}
.trap{background:#fff5f5;border:1px solid #ffd6d6;border-left:4px solid var(--hot);padding:12px 14px;border-radius:8px;font-size:13px;line-height:1.6}

/* ===== Frame Diagram ===== */
.frame-diagram{max-width:280px;margin:16px auto;border:2px solid var(--accent);border-radius:8px;overflow:hidden}
.frame-row{padding:8px 14px;text-align:center;font-size:13px;border-bottom:1px solid var(--border);background:var(--bg2)}
.frame-row:last-child{border-bottom:0}
.frame-row.top{background:var(--accent);color:#fff;font-weight:600}
.frame-row.bot{background:#eef0fa;font-weight:600}

/* ===== Formula ===== */
.formula{background:var(--bg2);border:1px solid var(--border);border-radius:var(--radius);padding:20px;margin:16px 0}
.formula p{margin:8px 0;font-size:14px}

/* ===== Self-Test (interactive quiz) ===== */
.test-header{display:flex;justify-content:space-between;align-items:center;background:linear-gradient(135deg,var(--green),#0aa67c);color:#fff;border-radius:var(--radius);padding:18px 24px;margin:16px 0;flex-wrap:wrap;gap:16px}
.test-header h3{margin:0;font-size:16px;color:#fff}
.test-header .score{font-size:24px;font-weight:800}
.test-header .score small{font-size:12px;font-weight:400;opacity:.85}
.test-controls{display:flex;gap:8px;flex-wrap:wrap}
.btn{padding:7px 16px;border-radius:6px;border:0;cursor:pointer;font-size:13px;font-weight:600;transition:.15s;font-family:inherit}
.btn-primary{background:#fff;color:var(--accent2)}
.btn-primary:hover{background:#f0f0ff}
.btn-ghost{background:rgba(255,255,255,.18);color:#fff}
.btn-ghost:hover{background:rgba(255,255,255,.28)}
.btn-accent{background:var(--accent);color:#fff}
.btn-accent:hover{background:var(--accent2)}

.test-q{background:var(--bg2);border:1px solid var(--border);border-radius:var(--radius);padding:18px 22px;margin:14px 0;box-shadow:var(--shadow)}
.test-q .q-num{font-size:11px;color:var(--accent);font-weight:700;letter-spacing:1px}
.test-q .q-stem{font-size:14.5px;margin:6px 0 12px;font-weight:500}
.test-q .q-mode{display:inline-block;margin-left:8px;padding:2px 8px;border-radius:999px;background:#eef0fa;color:var(--accent2);font-size:11px;font-weight:700;vertical-align:middle}
.test-q .opts{display:flex;flex-direction:column;gap:8px}
.test-q .opt{display:flex;gap:10px;padding:9px 14px;border:1.5px solid var(--border);border-radius:8px;cursor:pointer;font-size:14px;transition:.15s;align-items:flex-start}
.test-q .opt:hover{border-color:var(--accent);background:#f5f6ff}
.test-q .opt input{margin-top:4px;accent-color:var(--accent)}
.test-q .opt.selected{border-color:var(--accent);background:#eef2ff}
.test-q .opt.pending{box-shadow:inset 0 0 0 1px rgba(67,97,238,.15)}
.test-q .opt.correct{background:#e8f8f1;border-color:var(--green)}
.test-q .opt.wrong{background:#fff0f0;border-color:var(--hot)}
.test-q .opt.missed{background:#f0fdf4;border-color:var(--green)}
.test-q .opt.disabled{cursor:default;pointer-events:none}
.test-q .test-actions{margin-top:12px;display:flex;justify-content:flex-end}
.test-q .explain{display:none;margin-top:12px;padding:10px 14px;background:#f0fdf4;border-left:3px solid var(--green);border-radius:6px;font-size:13.5px;line-height:1.7}
.test-q.answered .explain{display:block}
.test-q .badge-right{display:inline-block;padding:2px 8px;background:var(--green);color:#fff;border-radius:10px;font-size:11px;font-weight:700;margin-left:6px}
.test-q .badge-wrong{display:inline-block;padding:2px 8px;background:var(--hot);color:#fff;border-radius:10px;font-size:11px;font-weight:700;margin-left:6px}
.test-q.answered .btn-submit{display:none}

/* ===== Interactive demos ===== */
.demo-box{background:var(--bg2);border:1px solid var(--border);border-radius:var(--radius);padding:18px 22px;margin:16px 0;box-shadow:var(--shadow)}
.demo-box h3{color:var(--accent2);margin-top:0}
.demo-input{width:100%;padding:10px 14px;border:1.5px solid var(--border);border-radius:6px;font-family:var(--mono);font-size:13px;margin:6px 0}
.demo-input:focus{outline:0;border-color:var(--accent)}
.demo-grammar{font-family:var(--mono);background:#f0f2ff;padding:12px 16px;border-radius:6px;font-size:13px;line-height:1.8;white-space:pre-wrap;margin:8px 0}
.demo-result{margin-top:12px;background:#f0fdf4;border-left:3px solid var(--green);padding:14px 18px;border-radius:6px;font-size:13.5px;line-height:1.8;min-height:40px}
.demo-result.empty{background:#f5f6f8;border-left-color:var(--border);color:var(--text2);font-style:italic;font-family:var(--mono);font-size:13px;white-space:pre-wrap}
.demo-result .ff-row{margin:4px 0}
.demo-result .ff-table{width:100%;border-collapse:collapse;margin:6px 0 10px;font-size:13.5px}
.demo-result .ff-table th{background:var(--accent);color:#fff;padding:6px 12px;text-align:left;font-weight:500}
.demo-result .ff-table td{border:1px solid var(--border);padding:6px 12px;background:#fff}
.demo-result .ff-table td:first-child{font-weight:600;text-align:center;width:120px;background:#eef0fa}

/* ===== Responsive ===== */
@media(max-width:900px){
  .sidebar{width:220px}
  .content{margin-left:220px}
  .container{padding:24px 20px 60px}
  .weight-grid,.trap-grid{grid-template-columns:1fr}
  .hero-title{font-size:1.6rem}
}
@media(max-width:640px){
  .sidebar{display:none}
  .content{margin-left:0}
}