/* ============ OpenStudy — modern dark UI ============ */
*{box-sizing:border-box;margin:0;padding:0}
:root{
  --bg:#0b1020;--bg2:#0e1528;--panel:#131b31;--panel2:#182242;--line:#263156;
  --text:#eaf0fd;--muted:#93a0c4;--muted2:#68759c;
  --accent:#6d8bff;--accent2:#22d3ee;--good:#34d399;--bad:#f87171;--warn:#fbbf24;
  --grad:linear-gradient(120deg,#6d8bff,#22d3ee);
  --r:18px;--rs:12px;
  --shadow:0 18px 44px -18px rgba(3,8,26,.8);
}
html{scroll-behavior:smooth}
body{background:radial-gradient(1100px 520px at 85% -10%,rgba(109,139,255,.14),transparent 60%),radial-gradient(900px 480px at -10% 110%,rgba(34,211,238,.10),transparent 55%),var(--bg);color:var(--text);font:15px/1.6 "Segoe UI",system-ui,-apple-system,Roboto,"Helvetica Neue",sans-serif;-webkit-font-smoothing:antialiased}
a{color:var(--accent);text-decoration:none}
a:hover{color:#9db3ff}
img{display:block;max-width:100%}
h1,h2,h3,h4{line-height:1.25}
button{font:inherit;cursor:pointer}

.app{display:flex;min-height:100vh}

/* ---------- sidebar ---------- */
.sidebar{width:264px;flex:none;position:sticky;top:0;height:100vh;padding:26px 20px;background:linear-gradient(180deg,rgba(19,27,49,.92),rgba(11,16,32,.96));border-right:1px solid var(--line);backdrop-filter:blur(10px);z-index:30}
.brand{display:flex;align-items:center;gap:12px;margin-bottom:30px}
.brand-mark{width:42px;height:42px;border-radius:14px;background:var(--grad);display:grid;place-items:center;font-size:20px;color:#081020;box-shadow:0 8px 22px -6px rgba(109,139,255,.55)}
.brand strong{display:block;font-size:17px}
.brand small{color:var(--muted);font-size:12px}
.nav-label{font-size:11px;letter-spacing:.14em;text-transform:uppercase;color:var(--muted2);margin:0 6px 10px}
.nav{display:flex;flex-direction:column;gap:4px}
.page-nav-link{display:flex;align-items:center;gap:11px;padding:11px 12px;border-radius:12px;color:var(--muted);border:1px solid transparent;transition:.18s}
.page-nav-link:hover{background:var(--panel);color:var(--text)}
.page-nav-link.active{background:linear-gradient(120deg,rgba(109,139,255,.16),rgba(34,211,238,.10));border-color:rgba(109,139,255,.35);color:var(--text)}
.nav-icon{width:24px;text-align:center;opacity:.9}
.sidebar-note{margin-top:14px;padding:16px;border:1px dashed var(--line);border-radius:14px;color:var(--muted);font-size:13px;background:rgba(19,27,49,.5)}
.sidebar-note b{display:block;color:var(--text);margin-bottom:4px}

.main{flex:1;min-width:0;display:flex;flex-direction:column}
.content{width:100%;max-width:1180px;margin:0 auto;padding:10px 30px 60px;flex:1}

/* ---------- topbar ---------- */
.topbar{position:sticky;top:0;z-index:20;display:flex;align-items:center;gap:16px;padding:14px 30px;background:rgba(11,16,32,.85);backdrop-filter:blur(12px);border-bottom:1px solid var(--line)}
.crumb{color:var(--muted);font-size:13.5px}
.crumb b{color:var(--text)}
.crumb span{margin:0 6px;color:var(--muted2)}
.top-actions{margin-left:auto;display:flex;align-items:center;gap:12px}
.search{background:var(--panel);border:1px solid var(--line);border-radius:12px;padding:9px 14px;color:var(--text);width:240px;outline:none;transition:.18s}
.search:focus{border-color:var(--accent);box-shadow:0 0 0 3px rgba(109,139,255,.18)}
.search::placeholder{color:var(--muted2)}
.avatar{width:36px;height:36px;border-radius:50%;background:var(--grad);color:#081020;font-weight:700;display:grid;place-items:center;font-size:13px}
.mobile-menu{display:none;background:var(--panel);border:1px solid var(--line);color:var(--text);border-radius:10px;padding:7px 11px}

/* ---------- hero ---------- */
.hero2{display:grid;grid-template-columns:1.35fr 1fr;gap:26px;align-items:stretch;margin:34px 0 10px}
.hero2-text{padding:40px 34px;border-radius:26px;background:linear-gradient(135deg,rgba(109,139,255,.16),rgba(34,211,238,.07)),var(--panel);border:1px solid rgba(109,139,255,.28);box-shadow:var(--shadow)}
.eyebrow{display:inline-block;font-size:11.5px;font-weight:700;letter-spacing:.16em;text-transform:uppercase;color:#9db3ff;background:rgba(109,139,255,.14);border:1px solid rgba(109,139,255,.3);padding:6px 12px;border-radius:999px;margin-bottom:16px}
.hero2-text h1{font-size:clamp(30px,4vw,44px);font-weight:800;letter-spacing:-.01em;margin-bottom:14px}
.hero2-text h1 span{background:var(--grad);-webkit-background-clip:text;background-clip:text;color:transparent}
.hero2-text p{color:var(--muted);max-width:56ch}
.hero2-actions{display:flex;gap:12px;margin-top:24px;flex-wrap:wrap}
.hero2-stats{display:grid;grid-template-columns:1fr 1fr;gap:14px}
.stat{background:var(--panel);border:1px solid var(--line);border-radius:20px;padding:20px;display:flex;flex-direction:column;justify-content:center;gap:4px}
.stat-label{font-size:12px;color:var(--muted);text-transform:uppercase;letter-spacing:.08em}
.stat-value{font-size:27px;font-weight:800}
.stat-value.stat-day{font-size:19px}
.stat-sub{color:var(--muted2);font-size:15px;font-weight:600}
.stat-detail{font-size:12.5px;color:var(--muted2)}
.hero .date-pill,.date-pill{align-self:flex-start;background:var(--panel);border:1px solid var(--line);border-radius:999px;padding:9px 16px;color:var(--muted);font-size:13px}
.date-pill span{color:var(--text);font-weight:600}

/* ---------- hub ---------- */
.hub{margin:26px 0;padding:24px;border-radius:22px;background:var(--panel);border:1px solid var(--line)}
.hub-head h3,.hub h2,.exams-strip h2{font-size:19px;margin-bottom:4px}
.hub-head p{color:var(--muted);font-size:13.5px;margin-bottom:16px}
.hub-links{display:flex;flex-wrap:wrap;gap:10px}
.hub-links a{padding:10px 16px;border-radius:12px;background:var(--panel2);border:1px solid var(--line);color:var(--text);font-weight:600;font-size:13.5px;transition:.18s}
.hub-links a:hover{border-color:var(--accent);transform:translateY(-2px);box-shadow:0 10px 20px -10px rgba(109,139,255,.5)}

/* ---------- exams ---------- */
.exams-strip{margin:26px 0}
.exams-strip h2{margin-bottom:14px}
.exam-grid{display:grid;grid-template-columns:repeat(auto-fit,minmax(230px,1fr));gap:14px}
.exam-card{display:block;background:var(--panel);border:1px solid var(--line);border-radius:16px;padding:18px;transition:.18s}
.exam-card b{display:block;font-size:16px;margin-bottom:4px;color:var(--text)}
.exam-card span{font-size:12.5px;color:var(--muted)}
.exam-card:hover{border-color:var(--accent2);transform:translateY(-2px)}

/* ---------- section head & chips ---------- */
.section-head{display:flex;align-items:flex-end;justify-content:space-between;gap:16px;margin:34px 0 18px}
.section-head h2{font-size:22px}
.section-head p{color:var(--muted);font-size:13.5px;margin-top:3px}
.text-btn{color:var(--accent);font-weight:600;font-size:13.5px;white-space:nowrap}
.chip-row{display:flex;gap:9px;flex-wrap:wrap;margin-bottom:20px}
.chip{padding:9px 17px;border-radius:999px;background:var(--panel);border:1px solid var(--line);color:var(--muted);font-weight:600;font-size:13.5px;transition:.18s}
.chip:hover{color:var(--text);border-color:#3a4a7d}
.chip.active{background:var(--grad);border-color:transparent;color:#081020}
.chip-fav.active{background:linear-gradient(120deg,#f472b6,#fbbf24)}

/* ---------- batch cards ---------- */
.batch-grid{display:grid;grid-template-columns:repeat(auto-fill,minmax(300px,1fr));gap:20px}
.bc{background:var(--panel);border:1px solid var(--line);border-radius:22px;overflow:hidden;display:flex;flex-direction:column;transition:.22s;position:relative}
.bc:hover{transform:translateY(-4px);border-color:rgba(109,139,255,.5);box-shadow:var(--shadow)}
.bc-media{position:relative;aspect-ratio:16/9;background:var(--panel2)}
.bc-media img{width:100%;height:100%;object-fit:cover;transition:.3s}
.bc:hover .bc-media img{transform:scale(1.04)}
.bc-fav{position:absolute;top:12px;right:12px;width:38px;height:38px;border-radius:50%;border:1px solid rgba(255,255,255,.25);background:rgba(8,12,26,.55);backdrop-filter:blur(6px);color:#fff;font-size:17px;line-height:1;display:grid;place-items:center;transition:.18s}
.bc-fav:hover{transform:scale(1.1);border-color:#f472b6;color:#f472b6}
.bc-fav.on{color:#f472b6;border-color:#f472b6}
.bc-body{padding:18px 18px 20px;display:flex;flex-direction:column;gap:9px;flex:1}
.bc-tags{display:flex;gap:8px}
.pill{font-size:11px;font-weight:700;letter-spacing:.06em;padding:4px 10px;border-radius:999px;text-transform:uppercase}
.pill-lang{background:rgba(34,211,238,.14);color:#67e8f9;border:1px solid rgba(34,211,238,.3)}
.pill-cat{background:rgba(109,139,255,.14);color:#9db3ff;border:1px solid rgba(109,139,255,.3)}
.bc h3{font-size:18.5px}
.bc h3 a{color:var(--text)}
.bc h3 a:hover{color:#cdddff}
.bc-sub{color:var(--muted);font-size:13.5px;display:-webkit-box;-webkit-line-clamp:2;-webkit-box-orient:vertical;overflow:hidden}
.bc-meta{display:flex;gap:8px;color:var(--muted2);font-size:12.5px}
.progress-line{height:6px;border-radius:99px;background:var(--panel2);overflow:hidden;margin-top:2px}
.progress-line i{display:block;height:100%;background:var(--grad);border-radius:99px}
.bc-cta{margin-top:8px;display:block;text-align:center;padding:12px;border-radius:13px;font-weight:700;color:var(--text);background:var(--panel2);border:1px solid var(--line);transition:.18s}
.bc-cta:hover{background:var(--grad);color:#081020;border-color:transparent}

/* ---------- workspace & batch page ---------- */
.workspace{display:grid;grid-template-columns:1.6fr 1fr;gap:24px;margin-top:24px;align-items:start}
.batch-hero{position:relative;border-radius:26px;overflow:hidden;border:1px solid var(--line);min-height:230px;display:flex;align-items:flex-end;margin-bottom:24px;background:var(--panel)}
.batch-hero-img{position:absolute;inset:0;width:100%;height:100%;object-fit:cover;opacity:.55}
.batch-hero-overlay{position:relative;padding:34px;background:linear-gradient(180deg,transparent,rgba(8,12,26,.88) 70%);width:100%}
.batch-hero-overlay h1{font-size:clamp(24px,3vw,34px);margin:6px 0 8px}
.batch-hero-overlay p{color:#c6d2ef;font-size:14px}
.batch-hero-overlay b{color:#fff}
.tag{display:inline-block;margin-top:12px;padding:7px 14px;border-radius:999px;background:rgba(8,12,26,.55);border:1px solid var(--line);font-size:12.5px;font-weight:600;color:var(--muted)}
.subject-row{display:grid;grid-template-columns:repeat(auto-fit,minmax(200px,1fr));gap:12px;margin-bottom:22px}
.subject-btn{display:flex;align-items:center;gap:12px;padding:14px;border-radius:15px;background:var(--panel);border:1px solid var(--line);transition:.18s}
.subject-btn:hover{border-color:#3a4a7d;transform:translateY(-2px)}
.subject-btn.selected{border-color:var(--accent);background:linear-gradient(120deg,rgba(109,139,255,.16),rgba(34,211,238,.08))}
.subject-btn small{display:block;color:var(--muted);font-size:12px}
.subject-icon{width:40px;height:40px;flex:none;border-radius:12px;background:var(--panel2);border:1px solid var(--line);display:grid;place-items:center;font-weight:800;font-size:13px;color:#9db3ff}
.chapter-panel,.detail,.schedule-card{background:var(--panel);border:1px solid var(--line);border-radius:20px;overflow:hidden}
.chapter-header,.detail-head{padding:20px 22px;border-bottom:1px solid var(--line);display:flex;align-items:center;justify-content:space-between;gap:14px;flex-wrap:wrap}
.chapter-header h2,.detail-head h2{font-size:18px}
.chapter-header span{color:var(--muted);font-size:13px}
.detail-head{display:block}
.detail-head p{color:var(--muted);font-size:13.5px;margin-top:4px}
.chapter-list{display:flex;flex-direction:column}
.chapter-row{display:flex;align-items:center;gap:16px;padding:16px 22px;border-bottom:1px solid var(--line);transition:.15s;color:var(--text)}
.chapter-row:last-child{border-bottom:0}
.chapter-row:hover{background:var(--panel2)}
.chapter-number{font-weight:800;color:var(--muted2);font-size:13px;width:26px}
.chapter-info{flex:1}
.chapter-info b{display:block;font-size:15px}
.chapter-info small{color:var(--muted);font-size:12.5px}
.check{width:26px;height:26px;border-radius:50%;border:2px solid var(--line);display:grid;place-items:center;color:transparent;flex:none;font-size:13px}
.check.done{background:rgba(52,211,153,.18);border-color:var(--good);color:var(--good)}

/* ---------- chapter detail ---------- */
.back-btn{display:inline-flex;align-items:center;gap:6px;color:var(--muted);font-weight:600;font-size:13.5px;margin:18px 0 14px}
.back-btn:hover{color:var(--text)}
.chapter-breadcrumb{color:var(--muted2);font-size:13px;margin-bottom:18px}
.chapter-breadcrumb a{color:var(--muted)}
.chapter-breadcrumb a:hover{color:var(--text)}
.chapter-breadcrumb span{margin:0 7px}
.tabs{display:flex;gap:8px;margin-top:16px;flex-wrap:wrap}
.tab{padding:9px 18px;border-radius:999px;background:var(--panel2);border:1px solid var(--line);color:var(--muted);font-weight:600;font-size:13.5px}
.tab:hover{color:var(--text)}
.tab.active{background:var(--grad);color:#081020;border-color:transparent}
.detail-body{padding:24px 22px}
.resource-box{border:1px dashed #35427299;border-radius:16px;padding:26px;background:rgba(24,34,66,.45)}
.resource-kicker{font-size:11.5px;font-weight:700;letter-spacing:.14em;text-transform:uppercase;color:#67e8f9;margin-bottom:8px}
.resource-box h3{font-size:19px;margin-bottom:8px}
.resource-box p{color:var(--muted);font-size:14px;max-width:64ch}
.resource-actions{display:flex;gap:12px;margin-top:18px;flex-wrap:wrap}
.dpp-q{margin-top:24px;padding-top:20px;border-top:1px solid var(--line)}
.dpp-q:first-of-type{margin-top:14px;padding-top:0;border-top:0}
.dpp-q h4{font-size:15.5px;margin-bottom:12px}
.options{display:grid;grid-template-columns:1fr 1fr;gap:10px}
.option-form{margin:0}
.option{width:100%;text-align:left;padding:13px 16px;border-radius:12px;background:var(--panel);border:1px solid var(--line);color:var(--text);font-size:14px;transition:.15s}
.option-submit:hover{border-color:var(--accent);background:var(--panel2)}
.option.correct{background:rgba(52,211,153,.15);border-color:var(--good)}
.option.wrong{background:rgba(248,113,113,.13);border-color:var(--bad)}
.dpp-result{margin-top:10px;font-size:13.5px;color:var(--muted)}
.mark-row{display:flex;align-items:center;gap:14px;margin-top:24px;flex-wrap:wrap}
.tiny-muted{color:var(--muted2);font-size:12.5px}
.simple-form{margin:0}

/* ---------- buttons & misc ---------- */
.primary-btn{display:inline-block;padding:12px 22px;border-radius:13px;background:var(--grad);color:#081020;font-weight:700;border:0;transition:.18s}
.primary-btn:hover{filter:brightness(1.12);color:#081020}
.outline-btn{display:inline-block;padding:11px 20px;border-radius:13px;background:transparent;border:1px solid var(--line);color:var(--text);font-weight:600;transition:.18s}
.outline-btn:hover{border-color:var(--accent);color:#cdddff}
.notice{padding:14px 18px;border-radius:13px;background:rgba(251,191,36,.1);border:1px solid rgba(251,191,36,.4);color:#fde68a;font-size:14px;margin:14px 0}
.notice.success{background:rgba(52,211,153,.1);border-color:rgba(52,211,153,.4);color:#a7f3d0}
.empty{padding:44px 22px;text-align:center;color:var(--muted);background:var(--panel);border:1px dashed var(--line);border-radius:18px;margin:20px 0}
.empty h2{color:var(--text);margin-bottom:10px}
.source-line{margin-top:18px;color:var(--muted2);font-size:12.5px}
.footer-note{text-align:center;color:var(--muted2);font-size:12px;padding:22px;border-top:1px solid var(--line)}

/* ---------- schedule ---------- */
.schedule-card{padding:24px;margin-top:26px}
.schedule-card h2{font-size:19px;margin-bottom:4px}
.schedule-card>p{color:var(--muted);font-size:13.5px;margin-bottom:16px}
.schedule-list{display:flex;flex-direction:column;gap:9px;margin-bottom:18px}
.schedule-item{display:flex;align-items:center;gap:12px;padding:12px 14px;border-radius:13px;background:var(--panel2);border:1px solid var(--line)}
.schedule-item input[type=checkbox]{width:17px;height:17px;accent-color:var(--accent)}
.schedule-item.done{opacity:.62}
.schedule-item.done .schedule-title{text-decoration:line-through}
.day-dot{flex:none;width:44px;text-align:center;font-size:11px;font-weight:800;letter-spacing:.06em;padding:6px 0;border-radius:9px;background:rgba(109,139,255,.14);color:#9db3ff;border:1px solid rgba(109,139,255,.3)}
.schedule-title{flex:1;font-size:14px;font-weight:600}
.schedule-title .schedule-sub{display:block;font-weight:400;color:var(--muted);font-size:12.5px;text-decoration:none}
.schedule-save{margin-top:6px}
.schedule-actions{display:flex;justify-content:flex-end;gap:12px;margin-top:18px}
.schedule-form .schedule-item{margin-bottom:9px;cursor:pointer}

/* ---------- responsive ---------- */
@media (max-width:1000px){
  .hero2{grid-template-columns:1fr}
  .workspace{grid-template-columns:1fr}
  .options{grid-template-columns:1fr}
}
@media (max-width:860px){
  .sidebar{position:fixed;left:-290px;transition:.25s;box-shadow:var(--shadow)}
  .sidebar.open{left:0}
  .mobile-menu{display:block}
  .search{width:150px}
  .content{padding:8px 16px 50px}
  .topbar{padding:12px 16px}
  .hero2-text{padding:28px 22px}
  .hero2-stats{grid-template-columns:1fr 1fr}
  .stat{padding:15px}
  .stat-value{font-size:21px}
  .crumb{display:none}
}