:root {
  --bg: #0d1117;
  --panel: #161b22;
  --panel-2: #1f2630;
  --border: #30363d;
  --text: #f0f3f6;
  --muted: #9da7b3;
  --accent: #79a8ff;
  --on-accent: #07101c;
  --good: #3fb950;
  --bad: #f85149;
  --warn: #d29922;
  --translation-bg: #10161e;
  --translation-text: #c9d7e8;
  --letter-bg: #252d38;
  --track: #242b35;
  color-scheme: dark;
}

/* Light palette: used when the system prefers light (unless dark is chosen) or when light is chosen explicitly. */
@media (prefers-color-scheme: light) {
  :root:not([data-theme="dark"]) {
    --bg: #f6f8fa;
    --panel: #ffffff;
    --panel-2: #eef1f5;
    --border: #d0d7de;
    --text: #1f2328;
    --muted: #59636e;
    --accent: #0b5fd6;
    --on-accent: #ffffff;
    --good: #1a7f37;
    --bad: #cf222e;
    --warn: #9a6700;
    --translation-bg: #eef4fc;
    --translation-text: #26405f;
    --letter-bg: #e4e9ef;
    --track: #dde3ea;
    color-scheme: light;
  }
}

:root[data-theme="light"] {
  --bg: #f6f8fa;
  --panel: #ffffff;
  --panel-2: #eef1f5;
  --border: #d0d7de;
  --text: #1f2328;
  --muted: #59636e;
  --accent: #0b5fd6;
  --on-accent: #ffffff;
  --good: #1a7f37;
  --bad: #cf222e;
  --warn: #9a6700;
  --translation-bg: #eef4fc;
  --translation-text: #26405f;
  --letter-bg: #e4e9ef;
  --track: #dde3ea;
  color-scheme: light;
}

* { box-sizing: border-box; }
[hidden] { display: none !important; }

body {
  margin: 0;
  background: var(--bg);
  color: var(--text);
  font-family: Inter, system-ui, -apple-system, "Segoe UI", sans-serif;
  line-height: 1.4;
}

button, input { font: inherit; }
button { color: inherit; }
:focus-visible { outline: 3px solid var(--accent); outline-offset: 2px; }

.shell { max-width: 1180px; margin: auto; padding: 22px; }
.top { display: flex; justify-content: space-between; gap: 18px; align-items: flex-start; }
h1 { margin: 0 0 4px; font-size: 25px; }
h2, h3 { margin: 0; }
.side h2 { font-size: 17px; margin-bottom: 10px; }
.side h3 { font-size: 15px; margin: 18px 0 8px; }
p { margin: 0; }
.muted, .small { color: var(--muted); }
.small { font-size: 13px; }

.badge { padding: 8px 11px; border: 1px solid var(--border); border-radius: 999px; background: var(--panel); font-size: 13px; white-space: nowrap; }
.notice { margin: 14px 0 0; padding: 10px 12px; border: 1px solid var(--border); border-radius: 10px; background: var(--panel); font-size: 13px; color: var(--muted); }

button {
  border: 1px solid var(--border);
  background: var(--panel);
  border-radius: 10px;
  padding: 10px 12px;
  cursor: pointer;
}
button:hover:not(:disabled) { background: var(--panel-2); }
button:disabled { opacity: .5; cursor: default; }
button.active, button.primary { background: var(--accent); color: var(--on-accent); border-color: transparent; font-weight: 700; }
button.primary:hover:not(:disabled), button.active:hover:not(:disabled) { background: var(--accent); filter: brightness(1.08); }
button.danger:hover:not(:disabled) { border-color: var(--bad); }

.tabs, .toolbar { display: flex; gap: 8px; flex-wrap: wrap; margin: 15px 0; }
select {
  font: inherit;
  color: inherit;
  border: 1px solid var(--border);
  background: var(--panel);
  border-radius: 10px;
  padding: 10px 12px;
  cursor: pointer;
}
select:hover { background: var(--panel-2); }
select.active { border-color: var(--accent); box-shadow: inset 0 0 0 1px var(--accent); font-weight: 700; }
.tabs .count { margin-left: 7px; padding: 1px 7px; border-radius: 99px; background: rgba(127, 127, 127, .25); font-size: 12px; }

.grid { display: grid; grid-template-columns: minmax(0, 1fr) 330px; gap: 18px; align-items: start; }
.card { background: var(--panel); border: 1px solid var(--border); border-radius: 15px; padding: 18px; }

.meta { display: flex; gap: 9px; flex-wrap: wrap; color: var(--muted); font-size: 13px; }
.q { font-size: 21px; font-weight: 700; line-height: 1.48; margin: 10px 0 14px; }

.translation { display: none; background: var(--translation-bg); border-left: 3px solid var(--accent); padding: 11px 12px; border-radius: 7px; margin: -3px 0 14px; line-height: 1.5; color: var(--translation-text); }
.translation.show { display: block; }
.langtag { font-size: 11px; text-transform: uppercase; letter-spacing: .08em; color: var(--accent); font-weight: 800; margin-right: 7px; }

.qimg { display: block; max-width: 100%; max-height: 560px; margin: 10px auto 15px; object-fit: contain; background: #fff; border-radius: 10px; }

.credit { margin: -8px 0 14px; text-align: center; }

.options { display: grid; gap: 9px; }
.option { width: 100%; text-align: left; padding: 13px 14px; display: flex; gap: 11px; align-items: flex-start; }
.letter { width: 27px; height: 27px; border-radius: 50%; background: var(--letter-bg); display: inline-flex; align-items: center; justify-content: center; font-weight: 800; flex: none; }
.enopt { display: block; margin-top: 4px; color: var(--muted); font-size: 13px; line-height: 1.35; font-weight: 400; }
.option.selected { border-color: var(--accent); box-shadow: inset 0 0 0 1px var(--accent); }
.option.correct { border-color: var(--good); background: color-mix(in srgb, var(--good) 14%, transparent); }
.option.wrong { border-color: var(--bad); background: color-mix(in srgb, var(--bad) 14%, transparent); }
.option:disabled { opacity: 1; }
.options .more { justify-self: start; }

.feedback { display: none; margin-top: 14px; padding: 13px; border-radius: 10px; line-height: 1.5; }
.feedback.show { display: block; }
.feedback.good { border: 1px solid color-mix(in srgb, var(--good) 55%, transparent); background: color-mix(in srgb, var(--good) 10%, transparent); }
.feedback.bad { border: 1px solid color-mix(in srgb, var(--bad) 55%, transparent); background: color-mix(in srgb, var(--bad) 10%, transparent); }
.verdict { display: flex; gap: 6px; align-items: baseline; flex-wrap: wrap; }
.why { margin-top: 8px; font-size: 14px; }
.why.en { margin-top: 6px; color: var(--muted); }
.explain-toggle { display: block; margin-top: 8px; font-size: 13px; }

.footer { display: flex; justify-content: space-between; gap: 10px; margin-top: 16px; }

.exam-bar { margin: 12px 0 4px; padding: 12px; border: 1px solid var(--border); border-radius: 12px; background: var(--panel-2); }
.exam-head { display: flex; align-items: center; gap: 14px; flex-wrap: wrap; }
.exam-head .primary { margin-left: auto; }
.timer { font-size: 26px; font-weight: 800; font-variant-numeric: tabular-nums; }
.timer.warn { color: var(--warn); }
.timer.danger { color: var(--bad); }
.navigator { display: flex; flex-wrap: wrap; gap: 6px; margin-top: 10px; }
.nav-dot { min-width: 34px; padding: 6px 0; border-radius: 8px; font-size: 13px; text-align: center; }
.nav-dot.answered { border-color: var(--accent); }
.nav-dot.right { border-color: var(--good); background: color-mix(in srgb, var(--good) 22%, transparent); }
.nav-dot.miss { border-color: var(--bad); background: color-mix(in srgb, var(--bad) 22%, transparent); }
.nav-dot.current { outline: 2px solid var(--text); outline-offset: 1px; }

.result { margin: 12px 0 4px; padding: 14px; border-radius: 12px; display: grid; gap: 8px; justify-items: start; }
.result.pass { border: 1px solid var(--good); background: color-mix(in srgb, var(--good) 12%, transparent); }
.result.fail { border: 1px solid var(--bad); background: color-mix(in srgb, var(--bad) 12%, transparent); }

.stats { margin: 0 0 14px; display: grid; gap: 2px; }
.stats div { display: flex; justify-content: space-between; padding: 7px 0; border-bottom: 1px solid var(--border); }
.stats dt { color: var(--muted); }
.stats dd { margin: 0; font-weight: 700; }

.stack { display: flex; height: 10px; border-radius: 99px; overflow: hidden; background: var(--track); margin: 12px 0 8px; }
.legend { list-style: none; margin: 0 0 12px; padding: 0; display: grid; gap: 3px; font-size: 13px; color: var(--muted); }
.legend li { display: flex; align-items: center; gap: 8px; }
.legend b { margin-left: auto; color: var(--text); }
.swatch { width: 10px; height: 10px; border-radius: 3px; display: inline-block; }
.seg-new { background: #6e7681; }
.seg-b0 { background: var(--bad); }
.seg-b1 { background: #4c78c9; }
.seg-b2 { background: #5a8be0; }
.seg-b3 { background: #79a8ff; }
.seg-b4 { background: #56d4a2; }
.seg-b5 { background: var(--good); }

.jump { margin-top: 16px; }
.plan { margin-top: 16px; }
.plan input { width: 100%; padding: 9px 10px; border: 1px solid var(--border); border-radius: 10px; background: var(--bg); color: var(--text); color-scheme: inherit; }
.jump-row { display: flex; gap: 8px; margin-top: 4px; }
.jump input { width: 100%; padding: 9px 10px; border: 1px solid var(--border); border-radius: 10px; background: var(--bg); color: var(--text); }

.history { list-style: none; margin: 0; padding: 0; display: grid; gap: 6px; }
.history li { display: flex; justify-content: space-between; gap: 10px; align-items: baseline; }
.history .ok { color: var(--good); }
.history .bad { color: var(--bad); }

.toast { position: fixed; left: 50%; bottom: 20px; transform: translateX(-50%); max-width: calc(100vw - 32px); padding: 11px 16px; border-radius: 10px; background: var(--text); color: var(--bg); font-size: 14px; box-shadow: 0 6px 24px rgba(0, 0, 0, .35); z-index: 10; }
.foot { margin-top: 18px; }

.lang-short { display: none; }

@media (max-width: 900px) {
  .grid { grid-template-columns: 1fr; }
  .top { flex-direction: column; }
  /* The English toggle floats so it stays within reach while scrolling through a question. */
  .lang-toggle { position: fixed; right: 16px; bottom: calc(16px + env(safe-area-inset-bottom, 0px)); z-index: 5; padding: 12px 16px; border-radius: 999px; box-shadow: 0 4px 16px rgba(0, 0, 0, .3); }
  .lang-long { display: none; }
  .lang-short { display: inline; }
  .foot { margin-bottom: 64px; }
  .toast { bottom: calc(76px + env(safe-area-inset-bottom, 0px)); }
}

@media (max-width: 520px) {
  .shell { padding: 14px; }
  .q { font-size: 19px; }
  .tabs button, .tabs select, .toolbar button { flex: 1 1 auto; }
}

@media (prefers-reduced-motion: no-preference) {
  button { transition: background-color .12s, border-color .12s; }
}

.top-actions { display: flex; align-items: center; gap: 10px; flex-wrap: wrap; }
.intro { display: flex; justify-content: space-between; align-items: center; gap: 12px; flex-wrap: wrap; margin: 14px 0 0; padding: 12px 14px; border: 1px solid var(--accent); border-radius: 10px; background: color-mix(in srgb, var(--accent) 10%, var(--panel)); }
.intro-actions { display: flex; gap: 8px; }
button.link { border: 0; background: none; padding: 0; color: var(--accent); text-decoration: underline; cursor: pointer; font-size: inherit; }
button.link:hover:not(:disabled) { background: none; }

.guide { width: min(720px, calc(100vw - 24px)); max-height: calc(100vh - 32px); padding: 0; border: 1px solid var(--border); border-radius: 15px; background: var(--panel); color: var(--text); }
.guide::backdrop { background: rgba(0, 0, 0, .6); }
.guide[open] { display: flex; flex-direction: column; }
.guide-head { display: flex; justify-content: space-between; align-items: center; gap: 12px; padding: 16px 20px; border-bottom: 1px solid var(--border); }
.guide-head h2 { font-size: 19px; }
.guide-body { overflow-y: auto; padding: 4px 20px 22px; line-height: 1.55; }
.guide-body section { margin-top: 20px; }
.guide-body h3 { font-size: 16px; margin-bottom: 8px; }
.guide-body p { margin-top: 8px; }
.guide-body ul, .guide-body ol { margin: 0; padding-left: 22px; display: grid; gap: 6px; }
.defs { margin: 0; display: grid; gap: 10px; }
.defs dt { font-weight: 700; }
.defs dd { margin: 2px 0 0; color: var(--muted); }
.boxes { width: 100%; margin-top: 10px; border-collapse: collapse; font-size: 14px; }
.boxes th, .boxes td { text-align: left; padding: 7px 10px; border-bottom: 1px solid var(--border); }
.boxes th { color: var(--muted); font-weight: 600; }

.state-chip { border-color: var(--accent); max-width: 100%; }
.state-grid { display: grid; grid-template-columns: repeat(auto-fill, minmax(190px, 1fr)); gap: 8px; margin-top: 16px; }
.state-option { display: flex; flex-direction: column; align-items: flex-start; gap: 1px; text-align: left; padding: 10px 12px; }
.state-name { font-weight: 700; overflow-wrap: anywhere; }
.state-en { font-size: 12px; color: var(--muted); }
.state-option[aria-current="true"] { border-color: var(--accent); box-shadow: inset 0 0 0 1px var(--accent); }
.state-option[aria-current="true"]:disabled { opacity: 1; }
.state-locked { padding: 9px 12px; border: 1px solid var(--warn); border-radius: 10px; background: color-mix(in srgb, var(--warn) 12%, transparent); }

@media (max-width: 520px) {
  .state-grid { grid-template-columns: 1fr 1fr; }
}