:root{
  --color-primary:#1D4ED8;--color-primary-600:#2563EB;--color-primary-700:#1E40AF;
  --color-primary-50:#EFF4FF;--color-primary-100:#DBE6FF;
  --color-accent:#0EA5E9;--color-accent-50:#E0F2FE;
  --color-gray-50:#F8FAFC;--color-gray-100:#F1F5F9;--color-gray-200:#E2E8F0;
  --color-gray-300:#CBD5E1;--color-gray-400:#94A3B8;--color-gray-500:#64748B;
  --color-gray-600:#475569;--color-gray-700:#334155;--color-gray-800:#1E293B;
  --color-gray-900:#0F172A;
  --color-bg:#F6F8FB;--color-surface:#FFFFFF;--color-surface-2:#F8FAFC;
  --color-border:#E2E8F0;--color-border-strong:#CBD5E1;
  --color-success:#16A34A;--color-success-50:#DCFCE7;
  --color-warning:#D97706;--color-warning-50:#FEF3C7;
  --color-danger:#DC2626;--color-danger-50:#FEE2E2;
  --color-info:#0EA5E9;
  --shadow-xs:0 1px 2px rgba(15,23,42,.04);
  --shadow-sm:0 1px 3px rgba(15,23,42,.06),0 1px 2px rgba(15,23,42,.04);
  --shadow-md:0 4px 12px rgba(15,23,42,.08);
  --shadow-lg:0 10px 24px rgba(15,23,42,.10);
  --shadow-xl:0 20px 40px rgba(15,23,42,.14);
  --radius-sm:6px;--radius-md:10px;--radius-lg:14px;--radius-xl:20px;
  --sidebar-w:248px;--topbar-h:60px;
  --font:-apple-system,BlinkMacSystemFont,"PingFang SC","Microsoft YaHei","Segoe UI",Roboto,Helvetica,Arial,sans-serif;
}
*{box-sizing:border-box;margin:0;padding:0}
html,body{height:100%}
body{font-family:var(--font);background:var(--color-bg);color:var(--color-gray-800);
  font-size:15px;line-height:1.6;-webkit-font-smoothing:antialiased;}
.tnum{font-variant-numeric:tabular-nums}
a{color:var(--color-primary);text-decoration:none}
::-webkit-scrollbar{width:10px;height:10px}
::-webkit-scrollbar-thumb{background:var(--color-gray-300);border-radius:8px;border:2px solid transparent;background-clip:content-box}
::-webkit-scrollbar-thumb:hover{background:var(--color-gray-400);background-clip:content-box}

/* ---------- Layout ---------- */
.app-shell{display:flex;min-height:100vh}
.sidebar{width:var(--sidebar-w);flex:0 0 var(--sidebar-w);background:var(--color-primary-700);
  color:#fff;display:flex;flex-direction:column;position:fixed;top:0;left:0;bottom:0;z-index:100;
  transition:transform .25s ease;}
.sidebar .brand{display:flex;align-items:center;gap:10px;padding:18px 20px;border-bottom:1px solid rgba(255,255,255,.12);}
.sidebar .brand .logo{width:34px;height:34px;border-radius:9px;background:linear-gradient(135deg,#3B82F6,#0EA5E9);
  display:flex;align-items:center;justify-content:center;font-weight:800;font-size:16px;color:#fff;}
.sidebar .brand b{font-size:15px;font-weight:700;line-height:1.2}
.sidebar .brand small{display:block;font-size:11px;color:rgba(255,255,255,.6);font-weight:400}
.nav{flex:1;overflow-y:auto;padding:12px 12px;}
.nav-group{font-size:11px;text-transform:uppercase;letter-spacing:.06em;color:rgba(255,255,255,.45);
  padding:14px 12px 6px;font-weight:700}
.nav-item{display:flex;align-items:center;gap:10px;padding:10px 12px;border-radius:10px;
  color:rgba(255,255,255,.78);font-weight:500;cursor:pointer;font-size:14px;margin-bottom:2px;user-select:none}
.nav-item .ic{width:18px;text-align:center;opacity:.9}
.nav-item:hover{background:rgba(255,255,255,.10);color:#fff}
.nav-item.active{background:#fff;color:var(--color-primary-700);font-weight:700}
.nav-item.active .ic{color:var(--color-primary)}
.sidebar .me{padding:14px 16px;border-top:1px solid rgba(255,255,255,.12);display:flex;align-items:center;gap:10px;font-size:13px}
.sidebar .me .av{width:34px;height:34px;border-radius:50%;background:rgba(255,255,255,.18);display:flex;align-items:center;justify-content:center;font-weight:700}
.sidebar .me .role{color:rgba(255,255,255,.6);font-size:11px}

.main{flex:1;margin-left:var(--sidebar-w);min-width:0;display:flex;flex-direction:column}
.topbar{height:var(--topbar-h);background:rgba(255,255,255,.85);backdrop-filter:blur(8px);
  border-bottom:1px solid var(--color-border);display:flex;align-items:center;gap:14px;
  padding:0 24px;position:sticky;top:0;z-index:90}
.topbar .menu-btn{display:none;background:none;border:none;font-size:20px;cursor:pointer;color:var(--color-gray-700)}
.topbar h1{font-size:17px;font-weight:700;color:var(--color-gray-900)}
.topbar .spacer{flex:1}
.topbar .search{flex:0 1 320px;position:relative}
.topbar .search input{width:100%;padding:8px 12px 8px 34px;border:1px solid var(--color-border-strong);
  border-radius:999px;font:400 14px var(--font);background:#fff;color:var(--color-gray-800)}
.topbar .search input:focus{outline:none;border-color:var(--color-primary);box-shadow:0 0 0 3px var(--color-primary-50)}
.topbar .search .si{position:absolute;left:12px;top:50%;transform:translateY(-50%);color:var(--color-gray-400)}
.icon-btn{position:relative;width:38px;height:38px;border-radius:10px;display:flex;align-items:center;justify-content:center;
  background:#fff;border:1px solid var(--color-border);cursor:pointer;color:var(--color-gray-600);font-size:17px}
.icon-btn:hover{background:var(--color-gray-50)}
.icon-btn .dot{position:absolute;top:7px;right:8px;width:8px;height:8px;border-radius:50%;background:var(--color-danger);border:2px solid #fff}
.avatar{width:36px;height:36px;border-radius:50%;background:var(--color-primary-50);color:var(--color-primary-700);
  display:flex;align-items:center;justify-content:center;font-weight:700;cursor:pointer;border:1px solid var(--color-primary-100)}
.content{padding:24px;max-width:1320px;width:100%;margin:0 auto}

/* ---------- Cards / Grid ---------- */
.grid{display:grid;gap:20px}
.cols-4{grid-template-columns:repeat(4,1fr)}
.cols-3{grid-template-columns:repeat(3,1fr)}
.cols-2{grid-template-columns:repeat(2,1fr)}
.span-2{grid-column:span 2}
.card{background:var(--color-surface);border:1px solid var(--color-border);border-radius:14px;
  padding:20px;box-shadow:var(--shadow-sm)}
.card-h{display:flex;align-items:center;justify-content:space-between;margin-bottom:14px}
.card-h h3{font-size:16px;font-weight:700;color:var(--color-gray-900)}
.card-hover{transition:box-shadow .15s,transform .15s}
.card-hover:hover{box-shadow:var(--shadow-md);transform:translateY(-2px)}
.stat{display:flex;flex-direction:column;gap:6px}
.stat .label{font-size:13px;color:var(--color-gray-500);display:flex;align-items:center;gap:6px}
.stat .val{font-size:30px;font-weight:800;color:var(--color-gray-900);line-height:1.1}
.stat .delta{font-size:12px;font-weight:600}
.delta.up{color:var(--color-success)}.delta.down{color:var(--color-danger)}
.stat .ic{width:34px;height:34px;border-radius:10px;display:flex;align-items:center;justify-content:center;font-size:17px}
.ic.blue{background:var(--color-primary-50);color:var(--color-primary)}
.ic.green{background:var(--color-success-50);color:var(--color-success)}
.ic.amber{background:var(--color-warning-50);color:var(--color-warning)}
.ic.cyan{background:var(--color-accent-50);color:var(--color-accent)}

/* ---------- Buttons ---------- */
.btn{display:inline-flex;align-items:center;gap:8px;font:600 14px/1 var(--font);
  padding:10px 18px;border-radius:10px;border:1px solid transparent;cursor:pointer;transition:.15s;white-space:nowrap}
.btn-primary{background:var(--color-primary);color:#fff}
.btn-primary:hover{background:var(--color-primary-600)}
.btn-primary:active{background:var(--color-primary-700)}
.btn-secondary{background:#fff;color:var(--color-gray-700);border-color:var(--color-border-strong)}
.btn-secondary:hover{background:var(--color-gray-50);border-color:var(--color-gray-400)}
.btn-ghost{background:transparent;color:var(--color-primary);padding:8px 12px}
.btn-ghost:hover{background:var(--color-primary-50)}
.btn-danger{background:#fff;color:var(--color-danger);border-color:var(--color-danger-50)}
.btn-danger:hover{background:var(--color-danger-50)}
.btn-sm{padding:7px 12px;font-size:13px}
.btn-block{width:100%;justify-content:center}
.btn[disabled]{opacity:.5;cursor:not-allowed}

/* ---------- Inputs ---------- */
.field{margin-bottom:16px}
.field>label{display:block;font-size:13px;font-weight:600;color:var(--color-gray-700);margin-bottom:6px}
.field .req{color:var(--color-danger)}
.input{width:100%;font:400 14px/1.5 var(--font);color:var(--color-gray-800);background:#fff;
  border:1px solid var(--color-border-strong);border-radius:10px;padding:10px 12px;transition:.15s}
.input::placeholder{color:var(--color-gray-400)}
.input:focus{outline:none;border-color:var(--color-primary);box-shadow:0 0 0 3px var(--color-primary-50)}
select.input{cursor:pointer}
textarea.input{min-height:90px;resize:vertical}

/* ---------- Badge / Tag ---------- */
.badge{display:inline-flex;align-items:center;gap:4px;font:600 12px/1 var(--font);padding:4px 10px;border-radius:999px;white-space:nowrap}
.badge-success{background:var(--color-success-50);color:var(--color-success)}
.badge-warning{background:var(--color-warning-50);color:var(--color-warning)}
.badge-danger{background:var(--color-danger-50);color:var(--color-danger)}
.badge-info{background:var(--color-accent-50);color:var(--color-accent)}
.badge-neutral{background:var(--color-gray-100);color:var(--color-gray-600)}
.badge-primary{background:var(--color-primary-50);color:var(--color-primary-700)}

/* ---------- Table ---------- */
.table-wrap{overflow-x:auto;border-radius:14px;border:1px solid var(--color-border);background:#fff}
table.tbl{width:100%;border-collapse:collapse;font-size:14px;min-width:640px}
.tbl th{text-align:left;font-size:12px;font-weight:700;color:var(--color-gray-500);
  text-transform:uppercase;letter-spacing:.03em;padding:12px 16px;background:var(--color-gray-50);border-bottom:1px solid var(--color-border)}
.tbl td{padding:13px 16px;border-bottom:1px solid var(--color-border);color:var(--color-gray-700);vertical-align:middle}
.tbl tr:last-child td{border-bottom:none}
.tbl tbody tr:hover{background:var(--color-gray-50)}
.tbl .u{display:flex;align-items:center;gap:10px}
.tbl .u .av{width:32px;height:32px;border-radius:50%;background:var(--color-primary-50);color:var(--color-primary-700);
  display:flex;align-items:center;justify-content:center;font-weight:700;font-size:13px;flex:0 0 auto}
.row-actions{display:flex;gap:8px}

/* ---------- Tabs ---------- */
.tabs{display:flex;gap:4px;border-bottom:1px solid var(--color-border);margin-bottom:20px;flex-wrap:wrap}
.tab{padding:10px 16px;font-weight:600;font-size:14px;color:var(--color-gray-500);cursor:pointer;border-bottom:2px solid transparent}
.tab:hover{color:var(--color-gray-800)}
.tab.active{color:var(--color-primary-700);border-bottom-color:var(--color-primary)}

/* ---------- Progress ---------- */
.progress{height:8px;background:var(--color-gray-200);border-radius:999px;overflow:hidden}
.progress>span{display:block;height:100%;background:linear-gradient(90deg,var(--color-primary),var(--color-accent));border-radius:999px;transition:width .4s}

/* ---------- Charts ---------- */
.chart{width:100%}
.chart svg{width:100%;height:auto;display:block}
.legend{display:flex;flex-wrap:wrap;gap:14px;margin-top:12px;font-size:13px;color:var(--color-gray-600)}
.legend i{display:inline-block;width:10px;height:10px;border-radius:3px;margin-right:6px;vertical-align:middle}

/* ---------- Course cards ---------- */
.course-grid{display:grid;grid-template-columns:repeat(3,1fr);gap:20px}
.course{background:#fff;border:1px solid var(--color-border);border-radius:14px;overflow:hidden;box-shadow:var(--shadow-sm);transition:.15s;cursor:pointer}
.course:hover{box-shadow:var(--shadow-md);transform:translateY(-2px)}
.course .cover{height:140px;background:linear-gradient(135deg,#1D4ED8,#0EA5E9);position:relative;display:flex;align-items:flex-end;padding:14px}
.course .cover .cat{background:rgba(255,255,255,.9);color:var(--color-primary-700);font-size:12px;font-weight:700;padding:4px 10px;border-radius:999px}
.course .cover .dur{position:absolute;top:12px;right:12px;background:rgba(15,23,42,.55);color:#fff;font-size:12px;padding:3px 8px;border-radius:999px}
.course .body{padding:14px}
.course .body h4{font-size:15px;font-weight:700;color:var(--color-gray-900);margin-bottom:6px}
.course .body .meta{font-size:13px;color:var(--color-gray-500);display:flex;justify-content:space-between;align-items:center}
.course .body .foot{margin-top:12px;display:flex;align-items:center;gap:10px}
.course .teacher{display:flex;align-items:center;gap:8px;font-size:13px;color:var(--color-gray-600)}
.course .teacher .av{width:26px;height:26px;border-radius:50%;background:var(--color-primary-50);color:var(--color-primary-700);display:flex;align-items:center;justify-content:center;font-weight:700;font-size:12px}

/* ---------- Login ---------- */
.auth-wrap{min-height:100vh;display:flex;align-items:center;justify-content:center;
  background:radial-gradient(1200px 600px at 20% -10%,#DBE6FF,transparent),radial-gradient(900px 500px at 100% 0%,#E0F2FE,transparent),var(--color-bg);
  padding:24px}
.auth-card{width:min(420px,100%);background:#fff;border-radius:20px;box-shadow:var(--shadow-xl);padding:32px}
.auth-card .brand{display:flex;align-items:center;gap:12px;margin-bottom:22px}
.auth-card .brand .logo{width:44px;height:44px;border-radius:12px;background:linear-gradient(135deg,#1D4ED8,#0EA5E9);
  display:flex;align-items:center;justify-content:center;font-weight:800;font-size:20px;color:#fff}
.auth-card .brand b{font-size:18px;color:var(--color-gray-900)}
.auth-card .brand small{display:block;font-size:12px;color:var(--color-gray-500);font-weight:400}
.auth-card h2{font-size:22px;font-weight:700;margin-bottom:4px}
.auth-card .sub{color:var(--color-gray-500);font-size:14px;margin-bottom:22px}
.role-pick{display:grid;grid-template-columns:repeat(3,1fr);gap:10px;margin-bottom:20px}
.role-opt{border:1.5px solid var(--color-border-strong);border-radius:12px;padding:14px 8px;text-align:center;cursor:pointer;transition:.15s}
.role-opt .em{font-size:22px}
.role-opt .nm{font-size:13px;font-weight:600;margin-top:4px;color:var(--color-gray-700)}
.role-opt.active{border-color:var(--color-primary);background:var(--color-primary-50)}
.auth-foot{margin-top:18px;text-align:center;font-size:13px;color:var(--color-gray-500)}
.auth-foot a{font-weight:600}

/* ---------- Modal ---------- */
.modal-overlay{position:fixed;inset:0;background:rgba(15,23,42,.45);display:flex;align-items:center;justify-content:center;z-index:1000;padding:20px;animation:fade .15s}
.modal{background:#fff;border-radius:16px;box-shadow:var(--shadow-xl);width:min(560px,100%);max-height:90vh;overflow:auto;animation:modalIn .18s ease}
.modal.wide{width:min(760px,100%)}
.modal-h{display:flex;align-items:center;justify-content:space-between;padding:18px 22px;border-bottom:1px solid var(--color-border)}
.modal-h h3{font-size:17px;font-weight:700}
.modal-h .x{background:none;border:none;font-size:22px;cursor:pointer;color:var(--color-gray-400);line-height:1}
.modal-b{padding:22px}
.modal-f{padding:16px 22px;border-top:1px solid var(--color-border);display:flex;justify-content:flex-end;gap:10px}
@keyframes modalIn{from{opacity:0;transform:translateY(8px)}to{opacity:1;transform:none}}
@keyframes fade{from{opacity:0}to{opacity:1}}

/* ---------- Toast ---------- */
#toast-root{position:fixed;top:18px;right:18px;z-index:1100;display:flex;flex-direction:column;gap:10px}
.toast{background:#fff;border:1px solid var(--color-border);border-left:4px solid var(--color-success);
  border-radius:10px;box-shadow:var(--shadow-lg);padding:12px 16px;font-size:14px;font-weight:600;color:var(--color-gray-800);
  display:flex;align-items:center;gap:10px;min-width:240px;animation:toastIn .2s ease}
.toast.success{border-left-color:var(--color-success)}
.toast.error{border-left-color:var(--color-danger)}
.toast.info{border-left-color:var(--color-info)}
.toast .ti{color:var(--color-success);font-size:16px}
.toast.error .ti{color:var(--color-danger)}.toast.info .ti{color:var(--color-info)}
@keyframes toastIn{from{opacity:0;transform:translateX(20px)}to{opacity:1;transform:none}}

/* ---------- Misc ---------- */
.page-head{display:flex;align-items:flex-end;justify-content:space-between;gap:16px;margin-bottom:22px;flex-wrap:wrap}
.page-head .h h1{font-size:26px;font-weight:800;color:var(--color-gray-900);letter-spacing:-.01em}
.page-head .h p{color:var(--color-gray-500);font-size:14px;margin-top:4px}
.toolbar{display:flex;gap:10px;flex-wrap:wrap;align-items:center;margin-bottom:18px}
.toolbar .grow{flex:1}
.pill{display:inline-flex;gap:6px;flex-wrap:wrap}
.empty{text-align:center;padding:50px 20px;color:var(--color-gray-400)}
.empty .em{font-size:40px}
.tree{font-size:14px}
.tree .node{padding:8px 10px;border-radius:8px;cursor:pointer;display:flex;align-items:center;gap:8px}
.tree .node:hover{background:var(--color-gray-50)}
.tree .node.active{background:var(--color-primary-50);color:var(--color-primary-700);font-weight:600}
.tree .children{margin-left:18px;border-left:1px solid var(--color-border);padding-left:8px}
.split{display:grid;grid-template-columns:300px 1fr;gap:20px;align-items:start}
.list-item{display:flex;align-items:center;gap:12px;padding:12px 14px;border:1px solid var(--color-border);border-radius:12px;margin-bottom:10px;cursor:pointer;transition:.15s}
.list-item:hover{border-color:var(--color-primary-100);background:var(--color-primary-50)}
.list-item.active{border-color:var(--color-primary);background:var(--color-primary-50)}
.list-item .av{width:40px;height:40px;border-radius:10px;background:var(--color-primary-50);color:var(--color-primary-700);display:flex;align-items:center;justify-content:center;font-weight:700;flex:0 0 auto}
.list-item .meta{flex:1;min-width:0}
.list-item .meta b{font-size:14px;color:var(--color-gray-900);display:block}
.list-item .meta small{font-size:12px;color:var(--color-gray-500)}
.flex{display:flex}.between{justify-content:space-between}.center{align-items:center}.gap8{gap:8px}.gap12{gap:12px}.gap16{gap:16px}.wrap{flex-wrap:wrap}
.mt8{margin-top:8px}.mt12{margin-top:12px}.mt16{margin-top:16px}.mt24{margin-top:24px}.mb8{margin-bottom:8px}.mb16{margin-bottom:16px}
.muted{color:var(--color-gray-500)}.small{font-size:13px}.center-text{text-align:center}
.q-opt{border:1px solid var(--color-border-strong);border-radius:10px;padding:12px 14px;margin-bottom:10px;cursor:pointer;display:flex;gap:10px;align-items:flex-start;transition:.15s}
.q-opt:hover{border-color:var(--color-primary)}
.q-opt.sel{border-color:var(--color-primary);background:var(--color-primary-50)}
.q-opt .mk{width:22px;height:22px;border-radius:50%;border:2px solid var(--color-gray-300);flex:0 0 auto;display:flex;align-items:center;justify-content:center;font-size:12px;font-weight:700;color:var(--color-gray-500)}
.q-opt.sel .mk{background:var(--color-primary);border-color:var(--color-primary);color:#fff}
.scroll-x{overflow-x:auto}
.section-title{font-size:15px;font-weight:700;color:var(--color-gray-800);margin:18px 0 10px}

/* ---------- Question bank / option editor ---------- */
.opt-row{transition:.15s}
.opt-row.sel .opt-key{background:var(--color-primary);border-color:var(--color-primary);color:#fff}
.opt-key{border:2px solid var(--color-gray-300);transition:.15s}
.opt-key:hover{border-color:var(--color-primary)}
.q-opt.q-multi .mk{border-radius:6px}
.q-opt.q-multi.sel .mk{background:var(--color-primary);color:#fff;content:""}

/* ---------- Media library ---------- */
.media-thumb{border-radius:8px;overflow:hidden;background:#0F172A}
.media-thumb video,.media-thumb img{display:block}
.kbd{font:600 12px var(--font);background:var(--color-gray-100);border:1px solid var(--color-border-strong);border-radius:6px;padding:2px 6px;color:var(--color-gray-600)}

/* ---------- Responsive ---------- */
@media(max-width:1024px){
  .course-grid{grid-template-columns:repeat(2,1fr)}
  .cols-4{grid-template-columns:repeat(2,1fr)}
  .cols-3{grid-template-columns:repeat(2,1fr)}
  .split{grid-template-columns:1fr}
}
@media(max-width:768px){
  .sidebar{transform:translateX(-100%)}
  .sidebar.open{transform:translateX(0);box-shadow:var(--shadow-xl)}
  .main{margin-left:0}
  .topbar .menu-btn{display:block}
  .topbar .search{display:none}
  .content{padding:16px}
  .course-grid{grid-template-columns:1fr}
  .cols-4,.cols-3,.cols-2{grid-template-columns:1fr}
  .span-2{grid-column:auto}
  .page-head .h h1{font-size:22px}
  .scrim{position:fixed;inset:0;background:rgba(15,23,42,.4);z-index:99;display:none}
  .scrim.show{display:block}
}