:root {
  --bg: #f6f7fb; --card: #fff; --text: #1b2333; --muted: #5d677b; --line: #e3e7f0;
  --brand: #2563eb; --ok: #15803d; --okbg: #e8f6ec; --bad: #b91c1c; --badbg: #fdecec; --skipbg: #fff6e0;
}
@media (prefers-color-scheme: dark) {
  :root {
    --bg: #11151f; --card: #1a2030; --text: #e8ecf6; --muted: #9aa5bb; --line: #2b344a;
    --brand: #6d9bff; --ok: #5ed487; --okbg: #15301f; --bad: #ff8585; --badbg: #381a1a; --skipbg: #38301a;
  }
}
* { box-sizing: border-box; }
body { margin: 0; background: var(--bg); color: var(--text); font: 16px/1.6 system-ui, "Segoe UI", Roboto, sans-serif; }
a { color: inherit; text-decoration: none; }
code { background: var(--line); padding: 1px 6px; border-radius: 5px; }
.top { background: var(--card); border-bottom: 1px solid var(--line); position: sticky; top: 0; z-index: 5; }
.top div { max-width: 980px; margin: auto; padding: 12px 16px; display: flex; align-items: center; gap: 12px; }
.top a { font-weight: 800; font-size: 18px; color: var(--brand); }
.top span { color: var(--muted); font-size: 14px; }
main { max-width: 980px; margin: auto; padding: 20px 16px 60px; }
.crumbs { font-size: 14px; color: var(--muted); margin-bottom: 12px; display: flex; flex-wrap: wrap; gap: 4px; }
.crumbs i { font-style: normal; margin: 0 4px; }
.crumbs a:hover { color: var(--brand); }
.hero { text-align: center; padding: 28px 0 22px; }
.hero h1 { font-size: 34px; margin: 0 0 8px; }
.hero p { color: var(--muted); max-width: 560px; margin: auto; }
.grade-grid { display: grid; grid-template-columns: repeat(auto-fit, minmax(210px, 1fr)); gap: 16px; }
.grade-card { background: var(--card); border: 1px solid var(--line); border-radius: 16px; padding: 24px; text-align: center; transition: transform .15s, box-shadow .15s; }
.grade-card:hover { transform: translateY(-3px); box-shadow: 0 8px 24px rgba(0,0,0,.1); }
.grade-card b { display: block; font-size: 56px; line-height: 1; color: var(--brand); }
.grade-card span { display: block; font-weight: 700; margin-top: 6px; }
.grade-card small { color: var(--muted); }
.grade-card.soon { opacity: .7; }
.title { margin: 6px 0 14px; font-size: 24px; }
.title .ico { display: inline-grid; place-items: center; width: 38px; height: 38px; border-radius: 10px; background: var(--c); color: #fff; font-size: 20px; vertical-align: middle; }
.subj-grid { display: grid; grid-template-columns: repeat(auto-fill, minmax(190px, 1fr)); gap: 14px; }
.subj-card { background: var(--card); border: 1px solid var(--line); border-top: 4px solid var(--c); border-radius: 14px; padding: 16px; display: flex; flex-direction: column; gap: 4px; transition: transform .15s; }
.subj-card:hover { transform: translateY(-3px); }
.subj-card .ico { font-size: 28px; color: var(--c); line-height: 1.1; }
.subj-card b { font-size: 18px; }
.subj-card small { color: var(--muted); }
.bar { height: 6px; background: var(--line); border-radius: 3px; overflow: hidden; margin-top: 6px; }
.bar i { display: block; height: 100%; background: var(--c); }
.tabs { display: flex; gap: 6px; overflow-x: auto; border-bottom: 2px solid var(--line); margin-bottom: 14px; }
.tabs a { padding: 10px 14px; white-space: nowrap; color: var(--muted); font-weight: 600; border-bottom: 3px solid transparent; margin-bottom: -2px; }
.tabs a.on { color: var(--brand); border-color: var(--brand); }
.desc { color: var(--muted); margin: 0 0 12px; }
.note { background: var(--skipbg); border-radius: 10px; padding: 10px 14px; font-size: 14px; }
.empty { background: var(--card); border: 1px dashed var(--line); border-radius: 12px; padding: 28px; text-align: center; color: var(--muted); }
.set-list { display: grid; gap: 10px; }
.set { background: var(--card); border: 1px solid var(--line); border-radius: 12px; padding: 14px 16px; display: grid; grid-template-columns: 1fr auto; gap: 2px 12px; align-items: center; }
.set:hover { border-color: var(--brand); }
.set small { color: var(--muted); grid-column: 1; }
.set em { grid-column: 2; grid-row: 1 / span 2; font-style: normal; font-size: 13px; color: var(--ok); font-weight: 600; }
.set em.new { color: var(--brand); }
.set.off { opacity: .55; pointer-events: none; }
.tips { background: var(--card); border: 1px solid var(--line); border-radius: 12px; padding: 4px 18px 10px; margin-top: 18px; }
.quiz-head { display: flex; justify-content: space-between; align-items: center; gap: 12px; border-left: 6px solid var(--c); padding-left: 12px; margin-bottom: 14px; }
.quiz-head h2 { margin: 0; font-size: 22px; }
.clock-box { background: var(--card); border: 1px solid var(--line); border-radius: 10px; padding: 6px 12px; position: sticky; top: 64px; font-size: 18px; }
.theory { background: var(--card); border: 1px solid var(--line); border-radius: 12px; padding: 10px 16px; margin-bottom: 16px; }
.theory summary { cursor: pointer; font-weight: 700; }
.theory ul { margin: 8px 0; padding-left: 20px; }
.q { background: var(--card); border: 1px solid var(--line); border-radius: 12px; padding: 14px 16px; margin-bottom: 14px; }
.q h4 { margin: 0 0 10px; font-size: 16px; font-weight: 600; }
.q h4 em { font-style: normal; color: var(--brand); margin-right: 6px; }
.opts { display: grid; gap: 8px; }
.opt { text-align: left; font: inherit; color: inherit; background: transparent; border: 1.5px solid var(--line); border-radius: 10px; padding: 9px 12px; cursor: pointer; display: flex; gap: 10px; align-items: baseline; }
.opt span { font-weight: 700; color: var(--muted); min-width: 16px; }
.opt:hover:not(:disabled) { border-color: var(--brand); }
.opt.pick { border-color: var(--brand); background: rgba(37,99,235,.08); }
.opt.right { border-color: var(--ok); background: var(--okbg); }
.opt.wrong { border-color: var(--bad); background: var(--badbg); }
.opt:disabled { cursor: default; }
.exp { margin-top: 10px; border-radius: 10px; padding: 10px 14px; font-size: 15px; }
.exp p { margin: 4px 0 0; }
.exp.ok { background: var(--okbg); } .exp.bad { background: var(--badbg); } .exp.skip { background: var(--skipbg); }
.actions { display: flex; gap: 10px; margin-top: 18px; }
.btn { background: var(--brand); color: #fff; border: 0; border-radius: 10px; padding: 11px 22px; font: inherit; font-weight: 700; cursor: pointer; }
.btn.ghost { background: transparent; color: var(--text); border: 1.5px solid var(--line); }
.score { display: flex; gap: 18px; align-items: center; background: var(--card); border: 1px solid var(--line); border-radius: 14px; padding: 16px 20px; margin-bottom: 16px; }
.score h3 { margin: 0; } .score p { margin: 2px 0 0; color: var(--muted); }
.ring { --p: 0; width: 84px; height: 84px; border-radius: 50%; display: grid; place-items: center; background: conic-gradient(var(--brand) calc(var(--p) * 1%), var(--line) 0); position: relative; }
.ring::before { content: ""; position: absolute; inset: 8px; background: var(--card); border-radius: 50%; }
.ring b { position: relative; }
@media (max-width: 520px) { .hero h1 { font-size: 28px; } .quiz-head { flex-direction: column; align-items: flex-start; } }

/* ---- thanh người dùng, đăng nhập, quản lý ---- */
.top div { flex-wrap: wrap; }
#userbar { margin-left: auto; display: flex; align-items: center; gap: 14px; font-size: 14px; }
#userbar a { color: var(--brand); font-size: 14px; }
#userbar .who { font-weight: 600; }
.muted { color: var(--muted); }
button.link { background: none; border: 0; color: var(--muted); font: inherit; cursor: pointer; text-decoration: underline; padding: 0; }
.auth { max-width: 380px; margin: 40px auto; background: var(--card); border: 1px solid var(--line); border-radius: 16px; padding: 26px; }
.auth h2 { margin: 0 0 4px; }
label { display: block; font-size: 14px; font-weight: 600; margin: 12px 0 0; }
input, select, textarea { display: block; width: 100%; margin-top: 4px; padding: 9px 11px; font: inherit; color: var(--text); background: var(--bg); border: 1.5px solid var(--line); border-radius: 9px; }
input:focus, select:focus, textarea:focus { outline: none; border-color: var(--brand); }
label.chk { display: flex; gap: 8px; align-items: center; font-weight: 500; }
label.chk input { width: auto; margin: 0; }
.err { color: var(--bad); font-size: 14px; min-height: 20px; margin: 8px 0; }
.ok-msg { color: var(--ok); font-size: 14px; }
.warn { color: var(--bad); font-size: 14px; }
.auth .btn { width: 100%; margin-top: 4px; }
.stack .actions { margin-top: 6px; }
.btn.sm { padding: 7px 14px; font-size: 14px; }
.btn.danger { background: var(--bad); color: #fff; }
.stats { display: grid; grid-template-columns: repeat(auto-fit, minmax(170px, 1fr)); gap: 12px; margin-bottom: 16px; }
.stat { background: var(--card); border: 1px solid var(--line); border-radius: 12px; padding: 14px 16px; }
.stat small { color: var(--muted); display: block; }
.stat b { font-size: 30px; line-height: 1.2; display: block; }
.stat em { font-style: normal; font-size: 13px; color: var(--muted); }
.two { display: grid; grid-template-columns: repeat(auto-fit, minmax(300px, 1fr)); gap: 14px; margin-bottom: 16px; }
.panel { background: var(--card); border: 1px solid var(--line); border-radius: 12px; padding: 4px 16px 16px; margin-bottom: 16px; }
.two .panel { margin-bottom: 0; }
.panel h3 { margin: 14px 0 10px; font-size: 17px; }
.panel-head { display: flex; justify-content: space-between; align-items: center; flex-wrap: wrap; gap: 8px; }
.tools { display: flex; gap: 8px; flex-wrap: wrap; align-items: center; }
.tools input, .tools select { width: auto; margin: 0; min-width: 160px; }
.srow { display: grid; grid-template-columns: 90px 1fr 44px 62px; gap: 8px; align-items: center; margin: 6px 0; font-size: 14px; }
.srow .bar { margin: 0; } .srow small { color: var(--muted); text-align: right; }
.feed { list-style: none; margin: 0; padding: 0; font-size: 14px; }
.feed li { padding: 6px 0; border-bottom: 1px solid var(--line); }
.feed small { color: var(--muted); }
.table-wrap { overflow-x: auto; }
.tbl { width: 100%; border-collapse: collapse; font-size: 14px; }
.tbl th, .tbl td { text-align: left; padding: 8px 10px; border-bottom: 1px solid var(--line); white-space: nowrap; }
.tbl th { color: var(--muted); font-weight: 600; }
.tbl .num { text-align: right; }
.tbl .low { color: var(--bad); font-weight: 700; }
.tbl tr.off { opacity: .55; }
.tbl a:hover { color: var(--brand); }
.tag { background: var(--badbg); color: var(--bad); border-radius: 6px; padding: 2px 8px; font-size: 12px; }
.inline-form { display: flex; gap: 8px; flex-wrap: wrap; align-items: center; }
.inline-form input { width: auto; margin: 0; }
.modal { position: fixed; inset: 0; background: rgba(0,0,0,.5); display: grid; place-items: center; padding: 16px; z-index: 20; }
.modal .box { background: var(--card); border-radius: 14px; padding: 20px; width: min(560px, 100%); max-height: 90vh; overflow: auto; }
.modal h3 { margin-top: 0; }
@media print { .top, .actions, .crumbs { display: none; } .modal { position: static; background: none; } .modal .box { box-shadow: none; } body > main { display: none; } }
@media (max-width: 520px) { .grades { display: none; } .srow { grid-template-columns: 70px 1fr 40px 54px; } }

/* ---- kiểu ứng dụng điện thoại ---- */
.title-row { display: flex; justify-content: space-between; align-items: center; gap: 12px; }
#tabbar { display: none; }
body { -webkit-tap-highlight-color: transparent; overscroll-behavior-y: none; }
.btn, .opt, .set, .subj-card, .grade-card, .tabs a, #tabbar a { touch-action: manipulation; }
@media (max-width: 760px) {
  body { padding-bottom: calc(68px + env(safe-area-inset-bottom)); font-size: 16px; }
  body.in-quiz { padding-bottom: calc(16px + env(safe-area-inset-bottom)); }
  .top { padding-top: env(safe-area-inset-top); }
  .top div { padding: 10px 16px; }
  main { padding: 14px 14px 24px; }
  #userbar a { display: none; }
  #userbar .who { max-width: 140px; overflow: hidden; text-overflow: ellipsis; white-space: nowrap; }
  #tabbar { position: fixed; left: 0; right: 0; bottom: 0; z-index: 10; display: flex; background: var(--card); border-top: 1px solid var(--line); padding-bottom: env(safe-area-inset-bottom); }
  #tabbar[hidden], body.in-quiz #tabbar { display: none; }
  #tabbar a { flex: 1; display: flex; flex-direction: column; align-items: center; gap: 1px; padding: 8px 4px 7px; color: var(--muted); font-size: 12px; font-weight: 600; min-height: 56px; }
  #tabbar a i { font-style: normal; font-size: 22px; line-height: 1.2; filter: grayscale(1); opacity: .7; }
  #tabbar a.on { color: var(--brand); }
  #tabbar a.on i { filter: none; opacity: 1; }
  .hero { padding: 16px 0 12px; }
  .grade-grid { grid-template-columns: 1fr; gap: 10px; }
  .grade-card { display: grid; grid-template-columns: 64px 1fr; align-items: center; text-align: left; padding: 14px 18px; gap: 0 14px; }
  .grade-card b { grid-row: 1 / span 2; font-size: 44px; }
  .subj-grid { grid-template-columns: repeat(2, 1fr); gap: 10px; }
  .subj-card { padding: 14px; }
  .tabs { margin: 0 -14px 14px; padding: 0 14px; scrollbar-width: none; }
  .tabs::-webkit-scrollbar { display: none; }
  .set { padding: 16px; }
  .opt { padding: 13px 14px; font-size: 16px; min-height: 48px; }
  .q { padding: 14px; }
  .clock-box { position: sticky; top: calc(56px + env(safe-area-inset-top)); z-index: 4; align-self: stretch; text-align: center; }
  .actions { position: sticky; bottom: 0; background: var(--bg); padding: 10px 0 calc(10px + env(safe-area-inset-bottom)); margin-top: 14px; z-index: 3; }
  .actions .btn { flex: 1; text-align: center; }
  .stats { grid-template-columns: repeat(2, 1fr); }
  .stat b { font-size: 26px; }
  .tools { width: 100%; } .tools input, .tools select { flex: 1; min-width: 0; }
  .modal { align-items: end; padding: 0; }
  .modal .box { border-radius: 18px 18px 0 0; width: 100%; padding-bottom: calc(20px + env(safe-area-inset-bottom)); }
  /* bảng học sinh thành thẻ */
  #stu-rows tr { display: grid; grid-template-columns: 1fr 1fr; gap: 2px 10px; padding: 12px 0; border-bottom: 1px solid var(--line); }
  #stu-rows td { display: block; border: 0; padding: 0; white-space: normal; text-align: left; font-size: 13px; }
  #stu-rows td.nm { grid-column: 1 / -1; font-size: 16px; }
  #stu-rows td[data-l]::before { content: attr(data-l) ": "; color: var(--muted); }
  #stu-rows td.num { text-align: left; }
  .tbl thead:has(+ #stu-rows) { display: none; }
}
@media (max-width: 760px) { #userbar button.link { display: none; } }
@media (max-width: 760px) { .tools #q-search { flex: 1 1 100%; } .tools select { flex: 1 1 40%; } .tools .btn { flex: 1 1 auto; } }
.tabs { overflow-y: hidden; }
.q h4 { white-space: pre-wrap; }
.q h4 em { white-space: normal; }

/* ---- đăng nhập, ảnh đại diện, trang cá nhân ---- */
.auth { text-align: center; }
.auth form { text-align: left; }
.auth .logo { width: 64px; height: 64px; margin: 0 auto 8px; border-radius: 18px; display: grid; place-items: center; font-size: 34px; background: linear-gradient(135deg, #2563eb, #7c3aed); box-shadow: 0 8px 20px rgba(37,99,235,.3); }
.auth .small, .small { font-size: 13px; }
.pw { position: relative; display: block; }
.pw input { padding-right: 64px; }
.pw .eye { position: absolute; right: 6px; top: 50%; transform: translateY(-50%); margin-top: 2px; background: none; border: 0; color: var(--brand); font: inherit; font-size: 13px; font-weight: 600; cursor: pointer; padding: 6px 8px; }
.avatar { width: 72px; height: 72px; border-radius: 50%; display: grid; place-items: center; flex: none; background: hsl(var(--h) 62% 44%); color: #fff; font-weight: 800; font-size: 26px; letter-spacing: 1px; }
.avatar.sm { width: 30px; height: 30px; font-size: 12px; letter-spacing: 0; }
#userbar .me { display: flex; align-items: center; gap: 8px; color: inherit; }
.me-hero { display: flex; gap: 16px; align-items: center; background: var(--card); border: 1px solid var(--line); border-radius: 16px; padding: 18px; margin-bottom: 14px; }
.me-hero h2 { margin: 0; font-size: 22px; }
.me-hero p { margin: 2px 0; color: var(--brand); font-weight: 600; }
.me-hero small { color: var(--muted); }
.grid2 { display: grid; grid-template-columns: 1fr 1fr; gap: 0 12px; }
input:disabled { opacity: .7; cursor: not-allowed; }
.btn.danger-ghost { color: var(--bad); border-color: var(--bad); }
.feed li em { font-style: normal; font-weight: 700; margin-left: 4px; }
.feed li small { display: block; }
@media (max-width: 760px) { .grid2 { grid-template-columns: 1fr; } .me-hero { flex-direction: column; text-align: center; } .avatar { width: 64px; height: 64px; font-size: 22px; } .auth { margin: 16px auto; } }