:root {
  --primary: #2563eb;--primary-dark: #1d4ed8;--secondary: #7c3aed;
  --success: #16a34a;--danger: #dc2626;
  --bg: #f1f5f9;--card: #ffffff;--text: #1e293b;--muted: #64748b;
  --border: #e2e8f0;
  --shadow: 0 1px 3px rgba(0,0,0,.10),0 1px 2px rgba(0,0,0,.06);
  --shadow-md: 0 4px 6px -1px rgba(0,0,0,.10),0 2px 4px -1px rgba(0,0,0,.06);
}
*{box-sizing:border-box;}
body{background:var(--bg);color:var(--text);font-family:-apple-system,BlinkMacSystemFont,'Segoe UI',Roboto,sans-serif;margin:0;font-size:15px;}
a{color:inherit;text-decoration:none;}

/* Navbar */
.navbar{background:var(--primary);padding:10px 0;position:sticky;top:0;z-index:100;box-shadow:var(--shadow-md);}
.nav-inner{max-width:1280px;margin:0 auto;padding:0 16px;display:flex;align-items:center;gap:12px;flex-wrap:wrap;}
.brand{font-weight:800;font-size:1.25rem;color:#fff;white-space:nowrap;display:flex;align-items:center;gap:8px;}
.brand-logo{background:#fff;color:var(--primary);border-radius:8px;padding:2px 8px;font-weight:900;font-size:1rem;}
.nav-search{flex:1;min-width:200px;max-width:460px;display:flex;}
.nav-search input{width:100%;padding:8px 16px;border:none;border-radius:24px 0 0 24px;font-size:.95rem;outline:none;}
.nav-search button{padding:8px 16px;background:#ff6d00;color:#fff;border:none;border-radius:0 24px 24px 0;cursor:pointer;font-weight:600;}
.btn-app{background:#ff6d00;color:#fff!important;padding:7px 16px;border-radius:20px;font-weight:700;font-size:.85rem;white-space:nowrap;}
.btn-app:hover{background:#e65100;}
.nav-right{display:flex;gap:8px;align-items:center;margin-left:auto;}

/* Layout */
.page{max-width:1280px;margin:24px auto;padding:0 16px;display:grid;grid-template-columns:220px 1fr 220px;gap:20px;}
.page.no-right{grid-template-columns:220px 1fr;}
.page.full{grid-template-columns:1fr;}

/* Sidebar */
.sidebar{position:sticky;top:70px;max-height:calc(100vh - 90px);overflow-y:auto;scrollbar-width:thin;}
.sidebar-title{font-size:.7rem;font-weight:700;text-transform:uppercase;letter-spacing:1px;color:var(--muted);padding:8px 10px 4px;}
.t-link{display:flex;align-items:center;gap:8px;padding:6px 10px;border-radius:8px;font-size:.88rem;transition:all .15s;color:var(--text);}
.t-link:hover{background:rgba(37,99,235,.1);color:var(--primary);}
.t-link.active{background:var(--primary);color:#fff!important;}
.t-badge{width:26px;height:26px;border-radius:6px;display:flex;align-items:center;justify-content:center;font-size:.75rem;font-weight:700;color:#fff;flex-shrink:0;}
.t-count{margin-left:auto;font-size:.75rem;color:var(--muted);background:var(--border);border-radius:10px;padding:1px 6px;}
.t-link.active .t-count{background:rgba(255,255,255,.25);color:#fff;}

/* Question card (fully clickable) */
.q-card-link{display:block;text-decoration:none;color:inherit;margin-bottom:10px;}
.q-card{background:var(--card);border:1px solid var(--border);border-radius:12px;padding:14px 16px;box-shadow:var(--shadow);display:flex;gap:14px;transition:box-shadow .15s,transform .15s;}
.q-card-link:hover .q-card{box-shadow:var(--shadow-md);transform:translateY(-1px);}
.q-card-link:hover .q-title{color:var(--primary);}
.q-stats{display:flex;flex-direction:column;gap:6px;flex-shrink:0;width:54px;}
.stat-box{display:flex;flex-direction:column;align-items:center;padding:5px 4px;border-radius:8px;border:1px solid var(--border);}
.stat-box.green{background:#dcfce7;border-color:#86efac;color:#15803d;}
.stat-num{font-size:1rem;font-weight:700;line-height:1;}
.stat-lbl{font-size:.6rem;text-transform:uppercase;color:var(--muted);letter-spacing:.4px;}
.stat-box.green .stat-lbl{color:#15803d;}
.q-body{flex:1;min-width:0;}
.q-title{font-size:1rem;font-weight:600;color:var(--text);margin-bottom:6px;display:block;line-height:1.4;}
.q-math{font-size:.95rem;margin:4px 0;overflow:hidden;max-height:60px;}
.q-img-thumb{max-width:200px;max-height:100px;object-fit:contain;border-radius:6px;border:1px solid var(--border);margin:6px 0;display:block;}
.q-footer{display:flex;align-items:center;gap:8px;flex-wrap:wrap;margin-top:8px;}
.tag{display:inline-block;padding:2px 9px;border-radius:12px;font-size:.72rem;font-weight:600;color:#fff;opacity:.9;}
.q-meta{font-size:.75rem;color:var(--muted);margin-left:auto;}
.badge-answered{background:#dcfce7;color:#15803d;padding:2px 8px;border-radius:10px;font-size:.72rem;font-weight:700;}
.badge-unanswered{background:#fee2e2;color:#dc2626;padding:2px 8px;border-radius:10px;font-size:.72rem;font-weight:700;}

/* Toolbar */
.toolbar{background:var(--card);border:1px solid var(--border);border-radius:12px;padding:12px 16px;margin-bottom:14px;display:flex;align-items:center;justify-content:space-between;gap:10px;flex-wrap:wrap;box-shadow:var(--shadow);}
.toolbar-title{font-weight:700;font-size:1.1rem;}

/* Question detail */
.q-detail{background:var(--card);border:1px solid var(--border);border-radius:12px;padding:24px;box-shadow:var(--shadow);margin-bottom:16px;}
.q-detail-header{display:flex;justify-content:space-between;align-items:flex-start;margin-bottom:16px;padding-bottom:14px;border-bottom:1px solid var(--border);gap:12px;}
.q-detail-title{font-size:1.25rem;font-weight:700;flex:1;line-height:1.4;}
.detail-meta{color:var(--muted);font-size:.82rem;margin-top:6px;display:flex;align-items:center;gap:8px;flex-wrap:wrap;}
.q-content{margin:12px 0;}
.q-img-full{max-width:100%;border-radius:10px;border:1px solid var(--border);margin:12px 0;display:block;}
.q-latex{font-size:1.05rem;line-height:1.8;margin:8px 0;}
.user-chip{display:inline-flex;align-items:center;gap:6px;background:rgba(37,99,235,.08);padding:4px 10px;border-radius:20px;font-size:.82rem;font-weight:600;color:var(--primary);}
.avatar{width:26px;height:26px;border-radius:50%;display:flex;align-items:center;justify-content:center;font-size:.75rem;font-weight:700;color:#fff;}

/* Answers */
.section-title{font-size:1.1rem;font-weight:700;margin:20px 0 12px;display:flex;align-items:center;gap:8px;}
.answer-card{background:var(--card);border:1px solid var(--border);border-left:4px solid var(--primary);border-radius:0 12px 12px 0;padding:18px 20px;margin-bottom:12px;box-shadow:var(--shadow);}
.answer-card .ans-meta{color:var(--muted);font-size:.8rem;margin-bottom:12px;display:flex;align-items:center;gap:8px;flex-wrap:wrap;}
.answer-card .ans-img{max-width:100%;border-radius:8px;border:1px solid var(--border);margin:10px 0;display:block;}
.answer-card .ans-latex{font-size:1rem;line-height:1.75;margin:8px 0;}

/* Comments */
.comments-box{margin-top:12px;padding-top:10px;border-top:1px dashed var(--border);}
.comment{padding:6px 10px;background:var(--bg);border-radius:6px;margin-bottom:4px;font-size:.83rem;border-left:3px solid var(--border);line-height:1.5;}
.comment .com-img{max-width:100%;max-height:120px;object-fit:contain;border-radius:4px;margin-top:4px;display:block;}
.comment .com-latex{font-size:.88rem;}
.com-user{font-weight:600;color:var(--primary);}

/* Topic grid */
.topic-grid{display:grid;grid-template-columns:repeat(auto-fill,minmax(180px,1fr));gap:14px;margin-top:16px;}
.topic-card{background:var(--card);border:1px solid var(--border);border-radius:12px;padding:20px;display:block;transition:all .2s;box-shadow:var(--shadow);}
.topic-card:hover{transform:translateY(-3px);box-shadow:var(--shadow-md);}
.tc-icon{width:44px;height:44px;border-radius:10px;display:flex;align-items:center;justify-content:center;font-size:1.1rem;font-weight:800;color:#fff;margin-bottom:10px;}
.tc-name{font-weight:700;font-size:.92rem;margin-bottom:3px;}
.tc-count{font-size:.78rem;color:var(--muted);}

/* Right panel */
.right-panel{position:sticky;top:70px;max-height:calc(100vh - 90px);overflow-y:auto;}
.panel-card{background:var(--card);border:1px solid var(--border);border-radius:12px;padding:16px;margin-bottom:14px;box-shadow:var(--shadow);}
.panel-title{font-size:.75rem;font-weight:700;text-transform:uppercase;letter-spacing:.6px;color:var(--muted);margin-bottom:10px;}
.related-item{padding:7px 0;border-bottom:1px solid var(--border);font-size:.84rem;line-height:1.4;}
.related-item:last-child{border-bottom:none;}
.related-item a{color:var(--primary);display:block;}
.related-item a:hover{text-decoration:underline;}
.related-item .rel-meta{font-size:.72rem;color:var(--muted);margin-top:2px;}

/* Hero */
.hero{background:linear-gradient(135deg,#1d4ed8 0%,#7c3aed 100%);padding:52px 16px 44px;color:#fff;text-align:center;}
.hero h1{font-size:2.6rem;font-weight:800;margin-bottom:10px;}
.hero p{font-size:1.05rem;opacity:.9;margin-bottom:24px;}
.hero-search{max-width:580px;margin:0 auto 28px;display:flex;border-radius:28px;overflow:hidden;box-shadow:0 4px 24px rgba(0,0,0,.2);}
.hero-search input{flex:1;padding:12px 20px;border:none;font-size:1rem;outline:none;}
.hero-search button{padding:12px 24px;background:#ff6d00;color:#fff;border:none;font-weight:700;font-size:1rem;cursor:pointer;}
.stats-bar{display:flex;justify-content:center;gap:32px;flex-wrap:wrap;}
.stat-item{text-align:center;}
.stat-item .number{font-size:1.8rem;font-weight:800;}
.stat-item .lbl{font-size:.8rem;opacity:.8;}

/* Pagination */
.pager{display:flex;gap:5px;justify-content:center;margin-top:20px;}
.page-btn{padding:6px 12px;border-radius:8px;border:1px solid var(--border);background:var(--card);font-size:.85rem;cursor:pointer;color:var(--text);}
.page-btn.active{background:var(--primary);color:#fff;border-color:var(--primary);}

/* Footer */
footer{background:#0f172a;color:#94a3b8;text-align:center;padding:28px 16px;font-size:.85rem;margin-top:40px;}
footer a{color:#60a5fa;}
.footer-links{display:flex;justify-content:center;gap:20px;margin-bottom:10px;flex-wrap:wrap;}

/* Responsive */
@media(max-width:900px){
  .page,.page.no-right{grid-template-columns:1fr;}
  .sidebar,.right-panel{display:none;}
  .hero h1{font-size:1.8rem;}
}
@media(max-width:600px){
  .q-stats{display:none;}
}