:root {
  --bg: #0f1117;
  --bg-soft: #161925;
  --panel: #1b1f2e;
  --panel-2: #222739;
  --line: #2d3348;
  --txt: #e8eaf2;
  --muted: #959cb5;
  --accent: #7c6cf0;
  --accent-2: #5bd1b0;
  --ok: #3ecf8e;
  --bad: #f2555a;
  --warn: #f0b429;
  --radius: 12px;
}
html[data-theme='light'] {
  --bg: #f4f5f9;
  --bg-soft: #eceef5;
  --panel: #ffffff;
  --panel-2: #f6f7fb;
  --line: #dcdfeb;
  --txt: #1b1f2e;
  --muted: #666d85;
  --accent: #5b4ce0;
  --accent-2: #0e9c7c;
  --ok: #17874f;
  --bad: #c8262c;
  --warn: #9a6b00;
}

* { box-sizing: border-box; }
body {
  margin: 0;
  background: var(--bg);
  color: var(--txt);
  font: 15px/1.6 -apple-system, BlinkMacSystemFont, 'Segoe UI', Roboto, 'Noto Sans', Arial, sans-serif;
}
main { max-width: 1180px; margin: 0 auto; padding: 22px 18px 80px; }
h1 { font-size: 24px; margin: 0 0 6px; }
h2 { font-size: 17px; margin: 0 0 14px; }
h3 { font-size: 15px; margin: 0 0 8px; }
a { color: var(--accent); }
.muted { color: var(--muted); }
.small { font-size: 13px; }
.hidden { display: none !important; }

/* topbar */
.topbar {
  position: sticky; top: 0; z-index: 20;
  display: flex; align-items: center; gap: 12px;
  padding: 11px 18px;
  background: color-mix(in srgb, var(--bg) 88%, transparent);
  backdrop-filter: blur(8px);
  border-bottom: 1px solid var(--line);
}
.brand { display: flex; align-items: center; gap: 9px; font-size: 15px; }
.brand .dot { width: 10px; height: 10px; border-radius: 50%; background: linear-gradient(135deg, var(--accent), var(--accent-2)); }
.topbar-actions { margin-left: auto; display: flex; gap: 8px; }

/* buttons */
.btn {
  font: inherit; cursor: pointer;
  background: var(--panel-2); color: var(--txt);
  border: 1px solid var(--line); border-radius: 9px;
  padding: 9px 14px; transition: .12s;
}
.btn:hover { border-color: var(--accent); }
.btn.primary { background: var(--accent); border-color: var(--accent); color: #fff; }
.btn.primary:hover { filter: brightness(1.1); }
.btn.ghost { background: transparent; }
.btn.small { padding: 6px 11px; font-size: 13px; }
.btn:disabled { opacity: .45; cursor: not-allowed; }
.btn.chip.active { background: var(--accent); border-color: var(--accent); color: #fff; }

/* panels */
.panel { background: var(--panel); border: 1px solid var(--line); border-radius: var(--radius); padding: 18px; margin-bottom: 18px; }
.course-head { display: flex; flex-wrap: wrap; gap: 18px; align-items: flex-end; margin-bottom: 18px; }
.stats { display: flex; gap: 10px; flex-wrap: wrap; }
.stat { background: var(--panel); border: 1px solid var(--line); border-radius: 10px; padding: 9px 14px; }
.stat b { display: block; font-size: 19px; }

/* settings */
.settings { display: grid; grid-template-columns: repeat(auto-fit, minmax(210px, 1fr)); gap: 12px 16px; align-items: center; }
.field { display: flex; flex-direction: column; gap: 5px; font-size: 13px; color: var(--muted); }
.field select, .field input { font: inherit; padding: 8px 10px; border-radius: 8px; border: 1px solid var(--line); background: var(--panel-2); color: var(--txt); }
.check { display: flex; align-items: center; gap: 9px; font-size: 14px; }
.check input { width: 17px; height: 17px; accent-color: var(--accent); }

/* exam cards */
.exam-grid { display: grid; grid-template-columns: repeat(auto-fill, minmax(330px, 1fr)); gap: 14px; margin-bottom: 18px; }
.exam-card { background: var(--panel); border: 1px solid var(--line); border-radius: var(--radius); padding: 16px; display: flex; flex-direction: column; gap: 10px; }
.exam-card.mix { border-color: var(--accent); background: linear-gradient(160deg, color-mix(in srgb, var(--accent) 12%, var(--panel)), var(--panel)); }
.exam-card h3 { margin: 0; font-size: 15px; line-height: 1.4; }
.exam-card .meta { font-size: 13px; color: var(--muted); }
.exam-card .row { display: flex; gap: 8px; margin-top: auto; flex-wrap: wrap; }
.badge { display: inline-block; font-size: 12px; padding: 2px 8px; border-radius: 20px; border: 1px solid var(--line); background: var(--panel-2); color: var(--muted); }
.badge.best { color: var(--ok); border-color: color-mix(in srgb, var(--ok) 45%, var(--line)); }
.badge.resume { color: var(--warn); border-color: color-mix(in srgb, var(--warn) 45%, var(--line)); }

/* quiz */
.quizbar { display: flex; gap: 14px; align-items: center; flex-wrap: wrap; margin-bottom: 10px; }
.quizbar-left { min-width: 0; }
.quiz-title { font-weight: 600; }
.quizbar-right { margin-left: auto; display: flex; gap: 9px; align-items: center; }
.timer { font-variant-numeric: tabular-nums; font-size: 19px; font-weight: 600; padding: 5px 12px; border-radius: 9px; background: var(--panel); border: 1px solid var(--line); }
.timer.warn { color: var(--warn); border-color: var(--warn); }
.timer.danger { color: var(--bad); border-color: var(--bad); }
.progress { height: 5px; background: var(--panel-2); border-radius: 4px; overflow: hidden; margin-bottom: 16px; }
.progress > div { height: 100%; width: 0; background: linear-gradient(90deg, var(--accent), var(--accent-2)); transition: width .2s; }

.quiz-layout { display: grid; grid-template-columns: 1fr 230px; gap: 18px; align-items: start; }
@media (max-width: 880px) { .quiz-layout { grid-template-columns: 1fr; } }

.qcard { background: var(--panel); border: 1px solid var(--line); border-radius: var(--radius); padding: 20px; }
.qhead { display: flex; align-items: center; gap: 10px; flex-wrap: wrap; margin-bottom: 14px; }
.qnum { font-weight: 700; font-size: 15px; }
.qbody p { margin: 0 0 11px; }
.qbody pre { background: var(--panel-2); padding: 12px; border-radius: 8px; overflow-x: auto; }
.qbody code { background: var(--panel-2); padding: 1px 5px; border-radius: 5px; font-size: 13px; }

.options { display: flex; flex-direction: column; gap: 9px; margin: 16px 0 0; }
.opt {
  display: flex; gap: 11px; align-items: flex-start;
  border: 1px solid var(--line); border-radius: 10px; padding: 12px 14px;
  background: var(--panel-2); cursor: pointer; transition: .12s;
}
.opt:hover { border-color: var(--accent); }
.opt.sel { border-color: var(--accent); background: color-mix(in srgb, var(--accent) 16%, var(--panel-2)); }
.opt .mark { flex: 0 0 24px; height: 24px; border-radius: 7px; border: 1px solid var(--line); display: grid; place-items: center; font-size: 12px; font-weight: 700; background: var(--panel); }
.opt.sel .mark { background: var(--accent); color: #fff; border-color: var(--accent); }
.opt .txt { flex: 1; }
.opt.correct { border-color: var(--ok); background: color-mix(in srgb, var(--ok) 15%, var(--panel-2)); }
.opt.correct .mark { background: var(--ok); color: #fff; border-color: var(--ok); }
.opt.wrong { border-color: var(--bad); background: color-mix(in srgb, var(--bad) 14%, var(--panel-2)); }
.opt.wrong .mark { background: var(--bad); color: #fff; border-color: var(--bad); }
.opt.locked { cursor: default; }
.opt.locked:hover { border-color: inherit; }

.explain { margin-top: 18px; padding: 15px 16px; border-left: 3px solid var(--accent); background: var(--panel-2); border-radius: 0 10px 10px 0; }
.explain > .verdict { font-weight: 700; margin-bottom: 8px; }
.explain .verdict.ok { color: var(--ok); }
.explain .verdict.bad { color: var(--bad); }
.explain p { margin: 0 0 10px; }
.explain a { word-break: break-word; }

.qnav { display: flex; gap: 9px; margin-top: 16px; flex-wrap: wrap; }
.qnav .btn:last-child { margin-left: auto; }
.kbd-hint { margin-top: 12px; }
kbd { background: var(--panel-2); border: 1px solid var(--line); border-bottom-width: 2px; border-radius: 5px; padding: 1px 5px; font-size: 12px; }

/* palette */
.palette-wrap { background: var(--panel); border: 1px solid var(--line); border-radius: var(--radius); padding: 14px; position: sticky; top: 70px; }
.palette-head { display: flex; justify-content: space-between; align-items: baseline; margin-bottom: 10px; }
.palette { display: grid; grid-template-columns: repeat(auto-fill, minmax(34px, 1fr)); gap: 6px; }
.palette button {
  font: inherit; font-size: 13px; cursor: pointer; aspect-ratio: 1;
  border-radius: 7px; border: 1px solid var(--line); background: var(--panel-2); color: var(--muted);
}
.palette button.answered { background: color-mix(in srgb, var(--accent) 28%, var(--panel-2)); color: var(--txt); border-color: var(--accent); }
.palette button.flagged { box-shadow: inset 0 0 0 2px var(--warn); color: var(--txt); }
.palette button.cur { outline: 2px solid var(--accent-2); outline-offset: 1px; }
.legend { list-style: none; padding: 0; margin: 14px 0 0; font-size: 12px; color: var(--muted); display: flex; flex-direction: column; gap: 6px; }
.legend li { display: flex; align-items: center; gap: 7px; }
.sw { width: 13px; height: 13px; border-radius: 4px; border: 1px solid var(--line); display: inline-block; }
.sw.answered { background: color-mix(in srgb, var(--accent) 28%, var(--panel-2)); border-color: var(--accent); }
.sw.flagged { box-shadow: inset 0 0 0 2px var(--warn); }
.sw.blank { background: var(--panel-2); }

/* result */
.score-hero { display: flex; gap: 22px; align-items: center; flex-wrap: wrap; background: var(--panel); border: 1px solid var(--line); border-radius: var(--radius); padding: 22px; margin-bottom: 18px; }
.ring { --p: 0; width: 132px; height: 132px; border-radius: 50%; display: grid; place-items: center; flex: 0 0 auto;
  background: conic-gradient(var(--ring-c) calc(var(--p) * 1%), var(--panel-2) 0); }
.ring .inner { width: 104px; height: 104px; border-radius: 50%; background: var(--panel); display: grid; place-items: center; text-align: center; }
.ring .pct { font-size: 27px; font-weight: 700; line-height: 1.1; }
.verdict-big { font-size: 21px; font-weight: 700; margin-bottom: 6px; }
.verdict-big.pass { color: var(--ok); }
.verdict-big.fail { color: var(--bad); }
.result-actions { display: flex; gap: 9px; margin-top: 14px; flex-wrap: wrap; }

table { width: 100%; border-collapse: collapse; font-size: 14px; }
th, td { text-align: left; padding: 9px 10px; border-bottom: 1px solid var(--line); }
th { color: var(--muted); font-weight: 600; font-size: 13px; }
td.num, th.num { text-align: right; font-variant-numeric: tabular-nums; }
.bar { height: 7px; background: var(--panel-2); border-radius: 4px; overflow: hidden; min-width: 90px; }
.bar > div { height: 100%; background: var(--ok); }
.bar > div.low { background: var(--bad); }
.bar > div.mid { background: var(--warn); }

.review-head { display: flex; justify-content: space-between; gap: 12px; align-items: center; flex-wrap: wrap; margin-bottom: 14px; }
.review-filters { display: flex; gap: 7px; flex-wrap: wrap; }
.rev-item { border: 1px solid var(--line); border-radius: 10px; padding: 16px; margin-bottom: 12px; background: var(--panel-2); }
.rev-item.ok { border-left: 3px solid var(--ok); }
.rev-item.bad { border-left: 3px solid var(--bad); }
.rev-item.blank { border-left: 3px solid var(--muted); }
.rev-item .options { margin-top: 12px; }
.rev-item .opt { background: var(--panel); cursor: default; }

/* tooltip dịch tiếng Việt */
.vi-on [data-vi]:hover { background: color-mix(in srgb, var(--accent) 12%, transparent); border-radius: 5px; cursor: help; }
.vi-on [data-vi='0'] { text-decoration: underline dotted color-mix(in srgb, var(--muted) 60%, transparent); text-underline-offset: 3px; }
.vitip {
  position: fixed; z-index: 60; max-width: 560px; min-width: 240px;
  background: var(--panel); color: var(--txt);
  border: 1px solid var(--accent); border-radius: 10px;
  box-shadow: 0 12px 32px rgba(0, 0, 0, .4);
  font-size: 14.5px; line-height: 1.65;
  pointer-events: none; /* khi chỉ hover: không chặn click vào đáp án bên dưới */
}
.vitip.pinned { pointer-events: auto; } /* đã ghim: cho phép cuộn, bôi đen, đóng */
.vitip-head {
  display: flex; align-items: center; justify-content: space-between; gap: 10px;
  padding: 7px 12px; border-bottom: 1px solid var(--line);
  font-size: 12px; text-transform: uppercase; letter-spacing: .05em; color: var(--muted);
  background: var(--panel-2); border-radius: 9px 9px 0 0;
}
.vitip-close { background: none; border: 0; color: var(--muted); font-size: 18px; line-height: 1; cursor: pointer; padding: 0 2px; }
.vitip-close:hover { color: var(--txt); }
.vitip-body { padding: 11px 13px; max-height: 46vh; overflow-y: auto; }
.vitip-body.missing { color: var(--muted); font-style: italic; }
.vitip.pinned { border-color: var(--accent-2); }

.toast { position: fixed; left: 50%; bottom: 26px; transform: translateX(-50%); background: var(--panel); border: 1px solid var(--accent); color: var(--txt); padding: 11px 18px; border-radius: 10px; z-index: 50; box-shadow: 0 8px 26px rgba(0,0,0,.35); }