:root {
  --bg: #f7f6f2; --panel: #ffffff; --ink: #1f2328; --muted: #5d6670; --line: #dcd9d0;
  --accent: #2b6cb0; --accent-ink: #fff; --ok: #1f7a4d; --ok-bg: #e5f4ec; --warn: #8a5a00; --warn-bg: #fdf3dc;
  --bad: #9b2c2c; --bad-bg: #fbe9e7; --code-bg: #14181d; --code-ink: #e6edf3;
}
@media (prefers-color-scheme: dark) {
  :root {
    --bg: #15171a; --panel: #1e2125; --ink: #e8e6e1; --muted: #a0a7b0; --line: #343a41;
    --accent: #6aa5e6; --accent-ink: #0b1017; --ok: #6cc59a; --ok-bg: #16301f; --warn: #e5b85c; --warn-bg: #32290f;
    --bad: #f09a92; --bad-bg: #351a18; --code-bg: #0b0d10; --code-ink: #dce3ea;
  }
}
* { box-sizing: border-box; }
body { margin: 0; background: var(--bg); color: var(--ink); font: 16px/1.7 system-ui, "Noto Sans TC", "Microsoft JhengHei", sans-serif; }
.top { display: flex; flex-wrap: wrap; gap: 8px 24px; align-items: center; justify-content: space-between; padding: 10px 16px; background: var(--panel); border-bottom: 1px solid var(--line); }
.brand { font-weight: 700; color: var(--ink); text-decoration: none; }
nav { display: flex; flex-wrap: wrap; gap: 4px 16px; }
nav a { color: var(--muted); text-decoration: none; padding: 10px 6px; min-height: 44px; display: inline-flex; align-items: center; }
nav a:hover, nav a.on { color: var(--accent); }
.end-link { font-weight: 600; }
main { max-width: 860px; margin: 0 auto; padding: 20px 16px 64px; outline: none; }
h1 { font-size: 1.5rem; margin: .2em 0 .4em; }
h2 { font-size: 1.2rem; margin: 1.6em 0 .5em; }
h3 { font-size: 1.05rem; margin: 1.2em 0 .3em; }
p { margin: .5em 0; }
.muted { color: var(--muted); font-size: .92rem; }
.card { background: var(--panel); border: 1px solid var(--line); border-radius: 10px; padding: 14px 16px; margin: 12px 0; }
.grid { display: grid; grid-template-columns: repeat(auto-fit, minmax(170px, 1fr)); gap: 12px; }
.metric b { display: block; font-size: 1.7rem; line-height: 1.2; }
.metric span { font-size: .85rem; color: var(--muted); }
button, .btn { font: inherit; cursor: pointer; border: 1px solid var(--line); background: var(--panel); color: var(--ink); border-radius: 8px; padding: 9px 16px; min-height: 44px; line-height: 1.4; text-decoration: none; display: inline-flex; align-items: center; justify-content: center; text-align: center; }
button:hover:not(:disabled), .btn:hover { border-color: var(--accent); }
button:disabled { opacity: .5; cursor: not-allowed; }
button.primary, .btn.primary { background: var(--accent); color: var(--accent-ink); border-color: var(--accent); }
button:focus-visible, a:focus-visible, input:focus-visible, textarea:focus-visible, select:focus-visible { outline: 3px solid var(--accent); outline-offset: 2px; }
.row { display: flex; flex-wrap: wrap; gap: 8px; align-items: center; }
.badge { display: inline-block; font-size: .78rem; padding: 1px 9px; border-radius: 999px; border: 1px solid var(--line); color: var(--muted); }
.badge.mastered { color: var(--ok); border-color: var(--ok); background: var(--ok-bg); }
.badge.practiced { color: var(--accent); border-color: var(--accent); }
.badge.review_due { color: var(--warn); border-color: var(--warn); background: var(--warn-bg); }
.badge.learning { color: var(--ink); }
pre.code { background: var(--code-bg); color: var(--code-ink); border-radius: 8px; padding: 12px 14px; overflow-x: auto; font: 14px/1.6 ui-monospace, Consolas, monospace; margin: 8px 0; white-space: pre; }
.codelabel { font-size: .78rem; color: var(--muted); margin-top: 10px; }
input[type=text], input[type=number], input[type=email], input[type=password], textarea, select { font: inherit; width: 100%; min-height: 44px; padding: 8px 10px; border: 1px solid var(--line); border-radius: 8px; background: var(--panel); color: var(--ink); }
input[type=number] { width: 6em; }
textarea { min-height: 90px; font-family: inherit; }
label { display: block; margin: 8px 0 2px; }
label.inline { display: inline-flex; gap: 6px; align-items: center; margin-right: 12px; }
.opt { display: flex; gap: 10px; align-items: flex-start; padding: 12px; min-height: 48px; border: 1px solid var(--line); border-radius: 8px; margin: 6px 0; cursor: pointer; }
.opt:has(input:checked) { border-color: var(--accent); }
.opt.right { border-color: var(--ok); background: var(--ok-bg); }
.opt.wrong { border-color: var(--bad); background: var(--bad-bg); }
.fb { border-left: 4px solid var(--line); padding: 4px 12px; margin: 10px 0; }
.fb.ok { border-color: var(--ok); } .fb.no { border-color: var(--bad); } .fb.info { border-color: var(--accent); }
.timerbar { background: var(--panel); border-bottom: 1px solid var(--line); padding: 8px 16px; display: flex; flex-wrap: wrap; gap: 8px 14px; align-items: center; }
.timerbar .clock { font: 600 1.4rem ui-monospace, Consolas, monospace; }
.timerbar.focus { border-bottom-color: var(--accent); }
.timerbar.break { border-bottom-color: var(--ok); }
.notice { background: var(--warn-bg); color: var(--warn); padding: 8px 16px; font-size: .92rem; }
.task { display: flex; gap: 10px; align-items: flex-start; padding: 10px 0; border-top: 1px solid var(--line); }
.task:first-child { border-top: 0; }
.check { width: 1.4em; text-align: center; color: var(--ok); font-weight: 700; }
.week { display: flex; gap: 6px; margin: 6px 0; }
.week i { width: 26px; height: 26px; border-radius: 6px; border: 1px solid var(--line); display: grid; place-items: center; font-size: .75rem; font-style: normal; color: var(--muted); }
.week i.on { background: var(--ok-bg); border-color: var(--ok); color: var(--ok); }
.week i.today { outline: 2px solid var(--accent); }
table { border-collapse: collapse; width: 100%; font-size: .92rem; }
th, td { border: 1px solid var(--line); padding: 6px 8px; vertical-align: top; text-align: left; }
.hintbtn.due { border-color: var(--accent); }
dialog { border: 1px solid var(--line); border-radius: 12px; background: var(--panel); color: var(--ink); max-width: 520px; width: calc(100% - 32px); }
dialog::backdrop { background: rgba(0,0,0,.4); }
.end-screen { text-align: center; padding: 40px 0; }
@media (max-width: 560px) { .timerbar .clock { font-size: 1.2rem; } }
@media (prefers-reduced-motion: reduce) { * { animation: none !important; transition: none !important; } }

/* ---- 第二階段：可讀性與觸控區（審查 UX-003／UX-004） ---- */
input[type=radio], input[type=checkbox] { width: 24px; height: 24px; flex: none; margin: 2px 0 0; accent-color: var(--accent); }
label.inline { min-height: 44px; }
.brand { padding: 10px 0; display: inline-flex; align-items: center; min-height: 44px; }
.reading { max-width: 68ch; font-size: 1.05rem; line-height: 1.85; }
.reading h2 { margin-top: 1.8em; }
.reading li { margin: .35em 0; }
.reading pre.code { font-size: .95rem; }
.lessonnav { margin: 12px 0; }
.pager { justify-content: space-between; }
.research h2.rtitle { margin: 0; font-size: 1.1rem; }
.research summary { cursor: pointer; padding: 10px 0; min-height: 44px; display: flex; align-items: center; color: var(--accent); }
dl.kv { display: grid; grid-template-columns: 8em 1fr; gap: 6px 14px; margin: 6px 0 0; }
dl.kv dt { color: var(--muted); font-size: .9rem; }
dl.kv dd { margin: 0; }
ul.links { margin: 0; padding-left: 1.2em; }
ul.links a { display: inline-block; padding: 8px 0; min-height: 44px; }
.badge.rs-confirmed { color: var(--ok); border-color: var(--ok); background: var(--ok-bg); }
.badge.rs-partial { color: var(--warn); border-color: var(--warn); background: var(--warn-bg); }
.badge.rs-unverified { color: var(--bad); border-color: var(--bad); background: var(--bad-bg); }
.hintnote { margin: 6px 0 0; }
@media (max-width: 560px) {
  dl.kv { grid-template-columns: 1fr; gap: 2px; }
  dl.kv dd { margin-bottom: 8px; }
  main { padding: 16px 14px 56px; }
  .pager a.btn { width: 100%; }
}

a.backlink { display: inline-flex; align-items: center; min-height: 44px; padding: 0 4px; }

/* 手機：長選項的下拉選單不可超出畫面 */
select { max-width: 100%; }
label.inline { flex-wrap: wrap; max-width: 100%; }