:root{
  --paper:#E8E2CE; --paper-deep:#DCD4B9; --card:#FBF8EF; --card-2:#F3EEDF;
  --ink:#211D14; --ink-soft:#5B5646; --ink-faint:#8A836D; --line:#C6BEA0; --line-soft:#DAD3B9;
  --navy:#253157; --navy-bright:#3A4B85; --navy-bg:#DFE3EF;
  --red:#A6362A; --red-bg:#F3DAD3;
  --green:#3D7A55; --green-bg:#DCEBDD;
  --amber:#966B1E; --amber-bg:#F1E1BE;
  --radius:10px; --radius-sm:6px;
  --font-serif:'Source Serif 4', Georgia, serif;
  --font-sans:'IBM Plex Sans', system-ui, sans-serif;
  --font-mono:'IBM Plex Mono', 'Courier New', monospace;
}
@media (prefers-color-scheme: dark){
  :root{
    --paper:#18160F; --paper-deep:#111009; --card:#221F16; --card-2:#2A2619;
    --ink:#ECE5D3; --ink-soft:#B8AF95; --ink-faint:#847C64; --line:#42402C; --line-soft:#333120;
    --navy:#8FA3E3; --navy-bright:#AEBEEE; --navy-bg:#252D4A;
    --red:#E28E7E; --red-bg:#3E2620;
    --green:#8FCBA5; --green-bg:#1F3328;
    --amber:#E2B961; --amber-bg:#392C15;
  }
}
*{box-sizing:border-box;}
html,body{margin:0;padding:0;}
body{
  background:var(--paper); color:var(--ink); font-family:var(--font-sans);
  font-size:15px; line-height:1.5; min-height:100vh;
  background-image:linear-gradient(var(--line-soft) 1px, transparent 1px);
  background-size:100% 32px;
}
h1,h2,h3,h4{font-family:var(--font-serif); font-weight:600; margin:0 0 4px; letter-spacing:.2px;}
p{margin:0 0 10px;}
a{color:var(--navy);}
button{font-family:var(--font-sans); cursor:pointer;}
input,select,textarea{font-family:var(--font-sans); font-size:14px;}

#app{min-height:100vh; display:flex; flex-direction:column;}
.boot{display:flex; align-items:center; justify-content:center; height:100vh; color:var(--ink-soft); font-family:var(--font-mono);}

.topbar{
  background:var(--paper-deep); border-bottom:1px solid var(--line);
  padding:12px 20px; display:flex; align-items:center; justify-content:space-between; gap:12px; flex-wrap:wrap;
}
.brand{display:flex; align-items:baseline; gap:10px;}
.brand .mark{
  width:30px; height:30px; border:1.5px solid var(--navy); border-radius:50%;
  display:inline-flex; align-items:center; justify-content:center; font-family:var(--font-mono);
  font-weight:700; font-size:12px; color:var(--navy); flex:none;
}
.brand h1{font-size:18px; color:var(--navy);}
.brand .sub{font-size:11px; color:var(--ink-faint); text-transform:uppercase; letter-spacing:1px;}
.who{display:flex; align-items:center; gap:10px; font-size:13px;}
.who .name{font-weight:600;}
.who .role-tag{font-family:var(--font-mono); font-size:10px; padding:2px 7px; border-radius:20px; border:1px solid var(--line);}

.shell{display:flex; flex:1; min-height:0;}
.sidebar{
  width:200px; flex:none; background:var(--card-2); border-right:1px solid var(--line);
  padding:16px 10px; display:flex; flex-direction:column; gap:2px;
}
.sidebar button{
  background:none; border:none; text-align:left; padding:9px 12px; border-radius:var(--radius-sm);
  color:var(--ink-soft); font-size:13.5px; font-weight:500;
}
.sidebar button:hover{background:var(--paper-deep); color:var(--ink);}
.sidebar button.active{background:var(--navy); color:#fff;}

.main{flex:1; min-width:0; padding:22px 26px 60px; max-width:1180px;}
.main.narrow{max-width:760px; margin:0 auto;}

.card{background:var(--card); border:1px solid var(--line); border-radius:var(--radius); padding:18px 20px; margin-bottom:16px;}
.card-title{display:flex; align-items:center; justify-content:space-between; margin-bottom:14px; gap:10px; flex-wrap:wrap;}
.card-title h2{font-size:17px;}
.hint{color:var(--ink-faint); font-size:12.5px;}

.btn{
  display:inline-flex; align-items:center; gap:6px; padding:8px 14px; border-radius:var(--radius-sm);
  border:1px solid var(--line); background:var(--card); color:var(--ink); font-size:13.5px; font-weight:600;
  transition:transform .08s ease;
}
.btn:active{transform:scale(.97);}
.btn-primary{background:var(--navy); border-color:var(--navy); color:#fff;}
.btn-primary:hover{background:var(--navy-bright); border-color:var(--navy-bright);}
.btn-danger{background:var(--red-bg); border-color:var(--red); color:var(--red);}
.btn-ghost{background:transparent; border-color:transparent;}
.btn-ghost:hover{background:var(--paper-deep);}
.btn-sm{padding:5px 10px; font-size:12.5px;}
.btn[disabled]{opacity:.45; cursor:not-allowed;}

.field{margin-bottom:12px;}
.field label{display:block; font-size:12.5px; font-weight:600; color:var(--ink-soft); margin-bottom:5px;}
.field input[type=text], .field input[type=password], .field input[type=number],
.field input[type=datetime-local], .field select, .field textarea{
  width:100%; padding:9px 11px; border:1px solid var(--line); border-radius:var(--radius-sm);
  background:var(--card); color:var(--ink);
}
.field textarea{min-height:70px; resize:vertical; font-family:var(--font-sans);}
.row{display:flex; gap:12px; flex-wrap:wrap;}
.row > .field{flex:1; min-width:160px;}
.check{display:flex; align-items:center; gap:7px; font-size:13.5px; margin-bottom:8px;}

table{width:100%; border-collapse:collapse; font-size:13.5px;}
th,td{text-align:left; padding:9px 10px; border-bottom:1px solid var(--line-soft);}
th{font-family:var(--font-mono); font-size:11px; text-transform:uppercase; letter-spacing:.6px; color:var(--ink-faint); font-weight:600;}
tr:hover td{background:var(--card-2);}

.badge{display:inline-block; padding:2px 9px; border-radius:20px; font-size:11px; font-weight:600; font-family:var(--font-mono);}
.badge-navy{background:var(--navy-bg); color:var(--navy);}
.badge-green{background:var(--green-bg); color:var(--green);}
.badge-red{background:var(--red-bg); color:var(--red);}
.badge-amber{background:var(--amber-bg); color:var(--amber);}
.badge-grey{background:var(--card-2); color:var(--ink-faint); border:1px solid var(--line);}

.stamp{
  display:inline-block; padding:4px 12px; border:2px solid var(--red); color:var(--red);
  border-radius:5px; font-family:var(--font-mono); font-size:11px; font-weight:700; letter-spacing:1.2px;
  transform:rotate(-3deg); text-transform:uppercase;
}
.stamp.green{border-color:var(--green); color:var(--green);}
.stamp.grey{border-color:var(--ink-faint); color:var(--ink-faint); transform:rotate(-2deg);}
.stamp.amber{border-color:var(--amber); color:var(--amber);}

.empty{padding:30px 10px; text-align:center; color:var(--ink-faint);}
.empty .big{font-family:var(--font-serif); font-size:16px; color:var(--ink-soft); margin-bottom:4px;}

.toast{
  position:fixed; bottom:18px; right:18px; background:var(--ink); color:var(--paper);
  padding:10px 16px; border-radius:var(--radius-sm); font-size:13px; z-index:999; max-width:320px;
  box-shadow:0 6px 20px rgba(0,0,0,.25);
}

.modal-back{position:fixed; inset:0; background:rgba(20,18,12,.55); display:flex; align-items:flex-start; justify-content:center; padding:40px 16px; overflow:auto; z-index:500;}
.modal{background:var(--card); border:1px solid var(--line); border-radius:var(--radius); padding:22px 24px; max-width:640px; width:100%;}

.login-wrap{flex:1; display:flex; align-items:center; justify-content:center; padding:30px 16px;}
.login-card{width:100%; max-width:380px; background:var(--card); border:1px solid var(--line); border-radius:var(--radius); padding:30px 28px; text-align:center;}
.login-card .mark{
  width:52px; height:52px; border:2px solid var(--navy); border-radius:50%; margin:0 auto 14px;
  display:flex; align-items:center; justify-content:center; font-family:var(--font-mono); font-weight:700;
  color:var(--navy); font-size:18px;
}
.login-card h1{font-size:21px; margin-bottom:2px;}
.login-card .sub{color:var(--ink-faint); font-size:12.5px; margin-bottom:20px; letter-spacing:.4px;}
.login-card .field{text-align:left;}
.seed-note{margin-top:16px; font-size:11.5px; color:var(--ink-faint); font-family:var(--font-mono); border-top:1px dashed var(--line); padding-top:12px;}
.err-msg{background:var(--red-bg); color:var(--red); padding:8px 11px; border-radius:var(--radius-sm); font-size:13px; margin-bottom:12px;}

.q-block{border:1px solid var(--line); border-radius:var(--radius); padding:16px 18px; margin-bottom:14px; background:var(--card); scroll-margin-top:14px;}
.q-explanation{margin-top:12px; padding:10px 12px; background:var(--navy-bg); color:var(--ink); border-radius:var(--radius-sm); font-size:13.5px; line-height:1.55;}
.q-head{display:flex; gap:10px; align-items:flex-start; margin-bottom:12px;}
.q-num{font-family:var(--font-mono); font-weight:700; color:var(--navy); flex:none;}
.q-content{white-space:pre-wrap;}
.opts{display:flex; flex-direction:column; gap:8px;}
.opt-row{display:flex; align-items:center; gap:10px; cursor:pointer; padding:6px 8px; border-radius:var(--radius-sm);}
.opt-row:hover{background:var(--card-2);}
.bubble{
  width:26px; height:26px; border-radius:50%; border:1.6px solid var(--ink-faint); flex:none;
  display:flex; align-items:center; justify-content:center; font-family:var(--font-mono); font-size:12px; font-weight:700;
  color:var(--ink-faint);
}
.opt-row.selected .bubble{background:var(--navy); border-color:var(--navy); color:#fff;}
.opt-row.selected{background:var(--navy-bg);}
.opt-row.correct .bubble{background:var(--green); border-color:var(--green); color:#fff;}
.opt-row.correct{background:var(--green-bg);}
.opt-row.wrong .bubble{background:var(--red); border-color:var(--red); color:#fff;}
.opt-row.wrong{background:var(--red-bg);}

.navgrid{display:grid; grid-template-columns:repeat(auto-fill,minmax(34px,1fr)); gap:6px;}
.navgrid button{
  width:34px; height:34px; border-radius:50%; border:1.6px solid var(--line); background:var(--card);
  font-family:var(--font-mono); font-size:12px; font-weight:700; color:var(--ink-soft);
}
.navgrid button.answered{background:var(--navy); border-color:var(--navy); color:#fff;}

.exambar{
  position:sticky; top:0; z-index:20; background:var(--paper-deep); border-bottom:1px solid var(--line);
  padding:10px 20px; display:flex; align-items:center; justify-content:space-between; gap:14px; flex-wrap:wrap;
}
.timerbox{
  font-family:var(--font-mono); font-size:19px; font-weight:700; padding:5px 14px; border:1.6px solid var(--navy);
  border-radius:var(--radius-sm); color:var(--navy); letter-spacing:1px; background:var(--card);
}
.timerbox.warn{border-color:var(--red); color:var(--red);}
.warnbanner{background:var(--red-bg); color:var(--red); padding:8px 14px; font-size:13px; text-align:center;}

.exam-layout{display:flex; gap:20px; align-items:flex-start;}
.exam-main{flex:1; min-width:0;}
.exam-side{width:230px; flex:none; position:sticky; top:70px;}

.score-big{font-family:var(--font-mono); font-size:44px; font-weight:700; color:var(--navy);}
.stat-grid{display:grid; grid-template-columns:repeat(auto-fit,minmax(120px,1fr)); gap:10px;}
.stat-box{border:1px solid var(--line); border-radius:var(--radius-sm); padding:10px 12px; background:var(--card-2);}
.stat-box .n{font-family:var(--font-mono); font-size:20px; font-weight:700;}
.stat-box .l{font-size:11px; color:var(--ink-faint); text-transform:uppercase; letter-spacing:.5px;}

.bar-row{display:flex; align-items:center; gap:8px; margin-bottom:6px; font-size:12.5px;}
.bar-row .lab{width:150px; flex:none; overflow:hidden; text-overflow:ellipsis; white-space:nowrap; color:var(--ink-soft);}
.bar-track{flex:1; height:9px; background:var(--card-2); border-radius:6px; overflow:hidden;}
.bar-fill{height:100%; background:var(--red);}
.bar-fill.green{background:var(--green);}

.notif-wrap{position:relative;}
.notif-dropdown{
  position:absolute; right:0; top:38px; z-index:200; width:290px;
  background:var(--card); border:1px solid var(--line); border-radius:var(--radius); padding:14px;
  box-shadow:0 8px 24px rgba(0,0,0,.18);
}
.notif-dropdown p{margin:0 0 8px;}

.cal-card{max-width:520px;}
.cal-header{display:flex; align-items:center; gap:8px; margin-bottom:2px;}
.cal-header h3{font-size:15px; min-width:120px; text-align:center;}
.cal-header .btn{padding:4px 12px; font-size:15px; line-height:1;}
.cal-today-btn{margin-left:auto;}
.cal-grid{display:grid; grid-template-columns:repeat(7,1fr); gap:5px;}
.cal-grid.cal-dow{margin-bottom:4px;}
.cal-cell{
  aspect-ratio:1; display:flex; flex-direction:column; align-items:center; justify-content:center;
  font-size:13px; border-radius:8px; position:relative; color:var(--ink-soft); border:1.5px solid transparent;
}
.cal-daynum{line-height:1;}
.cal-cell.head{aspect-ratio:auto; font-family:var(--font-mono); font-size:10.5px; color:var(--ink-faint); font-weight:600; padding:2px 0;}
.cal-cell.empty{background:transparent;}
.cal-cell.today .cal-daynum{position:relative;}
.cal-cell.today{border-color:var(--navy); font-weight:700; color:var(--ink);}
.cal-cell.has-exam{background:var(--card-2); font-weight:600; cursor:pointer;}
.cal-cell.has-exam:hover{filter:brightness(1.06); transform:translateY(-1px);}
.cal-cell.has-exam.cal-open{background:var(--green-bg); color:var(--green);}
.cal-cell.has-exam.cal-upcoming{background:var(--amber-bg); color:var(--amber);}
.cal-cell.has-exam.cal-closed{background:var(--card-2); color:var(--ink-faint);}
.cal-cell.selected{border-color:var(--red); box-shadow:0 0 0 1.5px var(--red) inset;}
.cal-count{
  font-family:var(--font-mono); font-size:10px; font-weight:700; color:var(--red); margin-top:1px; line-height:1;
}
.cal-legend{display:flex; gap:14px; flex-wrap:wrap; font-size:11.5px; color:var(--ink-faint); margin:10px 0 12px;}
.cal-legend span{display:inline-flex; align-items:center; gap:5px;}
.cal-swatch{width:9px; height:9px; border-radius:3px; display:inline-block;}
.cal-swatch.cal-open{background:var(--green);}
.cal-swatch.cal-upcoming{background:var(--amber);}
.cal-swatch.cal-closed{background:var(--ink-faint);}
.cal-day-list{border-top:1px solid var(--line); padding-top:10px;}
.cal-exam-item{padding:8px 0; border-bottom:1px dashed var(--line-soft);}
.cal-exam-item:last-child{border-bottom:none;}

.mon-grid{display:grid; grid-template-columns:repeat(auto-fill,minmax(150px,1fr)); gap:10px;}
.mon-tile{border:2px solid var(--line); border-radius:var(--radius-sm); padding:10px 12px; background:var(--card);}
.mon-tile.mon-notstarted{opacity:.6;}
.mon-tile.mon-inprogress{border-color:var(--navy); background:var(--navy-bg);}
.mon-tile.mon-submitted{border-color:var(--green); background:var(--green-bg);}
.mon-name{font-weight:700; font-size:13.5px;}
.mon-status{font-size:11.5px; margin-top:4px;}
.mon-score{font-family:var(--font-mono); font-weight:700; font-size:16px; margin-top:4px;}

@media (max-width:820px){
  .shell{flex-direction:column;}
  .sidebar{width:100%; flex-direction:row; overflow-x:auto; border-right:none; border-bottom:1px solid var(--line);}
  .exam-layout{flex-direction:column;}
  .exam-side{width:100%; position:static;}
  .main{padding:16px;}
}

/* ---- làm bài trên điện thoại ---- */
.mobile-nav-toggle{display:none;}
.exam-backdrop{display:none;}
@media (max-width:640px){
  .exambar{padding:8px 12px; gap:8px;}
  .exambar > div:first-child{font-size:13px; min-width:0; overflow:hidden; text-overflow:ellipsis; white-space:nowrap;}
  .exambar .btn{display:none;} /* nút Nộp bài trên thanh trên ẩn đi, dùng thanh nổi dưới cùng thay thế */
  .timerbox{font-size:16px; padding:4px 10px;}
  .q-block{padding:14px 14px 16px;}
  .q-content{font-size:15.5px; line-height:1.55;}
  .opt-row{padding:10px 10px; gap:12px;}
  .bubble{width:30px; height:30px; font-size:13px;}
  .shortAns, textarea.shortAns, input.shortAns, .blankInput, .matchSel{font-size:16px !important;} /* >=16px để iOS không tự zoom khi gõ */

  .mobile-nav-toggle{
    display:flex; position:fixed; right:16px; bottom:78px; z-index:250;
    width:52px; height:52px; border-radius:50%; background:var(--navy); color:#fff; border:none;
    align-items:center; justify-content:center; font-family:var(--font-mono); font-weight:700; font-size:13px;
    box-shadow:0 4px 14px rgba(0,0,0,.28);
  }
  .exam-side{
    position:fixed; top:0; right:0; height:100dvh; width:84%; max-width:340px; z-index:260;
    transform:translateX(100%); transition:transform .22s ease; overflow-y:auto; border-radius:0;
    box-shadow:-6px 0 20px rgba(0,0,0,.25);
  }
  .exam-side.open{transform:translateX(0);}
  .exam-backdrop{
    display:block; position:fixed; inset:0; background:rgba(0,0,0,.4); z-index:255;
    opacity:0; pointer-events:none; transition:opacity .2s ease;
  }
  .exam-backdrop.open{opacity:1; pointer-events:auto;}
  .exam-side .btn[data-view="teacher-exams"], .exam-side button[data-action="submitExam"]{display:none;}

  .mobile-submit-bar{
    position:fixed; left:0; right:0; bottom:0; z-index:240; background:var(--paper-deep); border-top:1px solid var(--line);
    padding:10px 14px; display:flex; gap:10px; align-items:center; justify-content:space-between;
  }
  .mobile-submit-bar .btn{width:auto; flex:1;}
  .main{padding-bottom:88px;} /* chừa chỗ cho thanh nộp bài nổi phía dưới */
}

/* ---- trang giới thiệu (landing) ---- */
.landing{max-width:1080px; margin:0 auto; padding:0 24px 60px;}
.landing-top{
  display:flex; align-items:center; justify-content:space-between; padding:22px 0;
}
.landing-hero{
  text-align:center; padding:56px 16px 40px; position:relative;
}
.hero-badge{
  display:inline-block; padding:4px 14px; border:1px solid var(--line); border-radius:20px;
  font-family:var(--font-mono); font-size:11px; letter-spacing:1px; text-transform:uppercase;
  color:var(--navy); background:var(--card); margin-bottom:18px;
}
.landing-hero h1{
  font-size:clamp(26px,4vw,40px); line-height:1.25; max-width:760px; margin:0 auto 18px;
}
.hero-sub{
  max-width:600px; margin:0 auto 28px; color:var(--ink-soft); font-size:15.5px; line-height:1.6;
}
.hero-cta{display:flex; gap:12px; justify-content:center; flex-wrap:wrap; margin-bottom:44px;}
.hero-cta .btn{padding:11px 22px; font-size:14.5px;}

.omr-strip{
  max-width:280px; margin:0 auto; background:var(--card); border:1px solid var(--line);
  border-radius:var(--radius); padding:18px 22px; transform:rotate(-1.5deg); box-shadow:0 10px 28px rgba(0,0,0,.08);
}
.omr-row{display:flex; align-items:center; gap:10px; margin-bottom:9px;}
.omr-row:last-child{margin-bottom:0;}
.omr-num{width:16px; font-family:var(--font-mono); font-size:11px; color:var(--ink-faint); flex:none;}
.omr-bubble{
  width:20px; height:20px; border-radius:50%; border:1.4px solid var(--ink-faint);
  display:flex; align-items:center; justify-content:center; font-family:var(--font-mono);
  font-size:10px; font-weight:700; color:var(--ink-faint); flex:none;
}
.omr-bubble.filled{background:var(--navy); border-color:var(--navy); color:#fff;}

.landing-features{
  display:grid; grid-template-columns:repeat(auto-fit,minmax(230px,1fr)); gap:16px; margin-bottom:48px;
}
.feature-card{
  background:var(--card); border:1px solid var(--line); border-radius:var(--radius); padding:20px 20px 22px;
  transition:transform .15s ease, box-shadow .15s ease;
}
.feature-card:hover{transform:translateY(-3px); box-shadow:0 10px 22px rgba(0,0,0,.08);}
.feature-icon{font-size:26px; margin-bottom:10px;}
.feature-card h3{font-size:15px; margin-bottom:6px; color:var(--navy);}
.feature-card p{font-size:13px; color:var(--ink-soft); line-height:1.55; margin:0;}

.landing-footer{
  text-align:center; padding:32px 20px; border-top:1px dashed var(--line);
}
.landing-footer p{color:var(--ink-faint); font-size:13px; margin-bottom:16px;}

@media (max-width:640px){
  .landing-top{flex-wrap:wrap; gap:12px;}
  .landing-hero{padding:36px 8px 28px;}
}