/* formal-learning — 三層側欄 + 長文閱讀版面
   淺色為預設，深色只覆寫 token（見 :root 與 prefers-color-scheme） */

:root {
  --bg: #faf9f7;
  --bg-elev: #fff;
  --bg-side: #f3f1ed;
  --fg: #1c1a17;
  --fg-dim: #5f5a52;
  --fg-faint: #918a80;
  --line: #e0dcd4;
  --accent: #0f766e;
  --accent-soft: #d7ede9;
  --code-bg: #f1efea;
  --sans: "PingFang TC", "Noto Sans TC", "Hiragino Sans", system-ui, -apple-system, "Segoe UI", sans-serif;
  --mono: "SF Mono", "JetBrains Mono", "Cascadia Code", ui-monospace, Menlo, Consolas, monospace;
  --side-w: 264px;
}

@media (prefers-color-scheme: dark) {
  :root {
    --bg: #14161a;
    --bg-elev: #1a1d22;
    --bg-side: #101216;
    --fg: #e6e4e0;
    --fg-dim: #a8a49d;
    --fg-faint: #6f6b65;
    --line: #2a2e35;
    --accent: #5eead4;
    --accent-soft: #16332e;
    --code-bg: #1d2026;
  }
}

* { box-sizing: border-box; }

html { scroll-behavior: smooth; scroll-padding-top: 1.5rem; }

body {
  margin: 0;
  background: var(--bg);
  color: var(--fg);
  font-family: var(--sans);
  font-size: 17px;
  line-height: 1.8;
  -webkit-font-smoothing: antialiased;
}

a { color: var(--accent); text-decoration-thickness: 1px; text-underline-offset: 2px; }
a:hover { text-decoration-thickness: 2px; }

/* ---------------------------------------------------------------- 側欄 */

#side {
  position: fixed;
  inset: 0 auto 0 0;
  width: var(--side-w);
  padding: 1.5rem 0 1.5rem 1.25rem;
  background: var(--bg-side);
  border-right: 1px solid var(--line);
  overflow-y: auto;
  overscroll-behavior: contain;
  font-size: 15px;
  display: flex;
  flex-direction: column;
  gap: 2px;
}

.brand {
  font-weight: 700;
  font-size: 16px;
  letter-spacing: -0.01em;
  color: var(--fg);
  text-decoration: none;
  margin-bottom: 1.25rem;
  padding-right: 1.25rem;
}
.brand span { color: var(--fg-faint); font-weight: 400; }

#side > a,
.unit-head {
  display: flex;
  align-items: center;
  justify-content: space-between;
  gap: 0.5rem;
  padding: 0.4rem 1.25rem 0.4rem 0.6rem;
  margin-left: -0.6rem;
  border-radius: 6px;
  color: var(--fg-dim);
  text-decoration: none;
}
#side > a:hover,
.unit-head:hover { background: var(--bg-elev); color: var(--fg); }

#side > a.active,
.unit-head.active {
  color: var(--accent);
  font-weight: 600;
  background: var(--accent-soft);
}

.unit { margin-top: 2px; }

/* 第二層：節內錨點 */
.toc {
  list-style: none;
  margin: 0.25rem 0 0.6rem;
  padding: 0 0 0 0.6rem;
  border-left: 2px solid var(--line);
}
.toc a {
  display: block;
  padding: 0.22rem 0.5rem;
  color: var(--fg-dim);
  text-decoration: none;
  font-size: 14px;
  line-height: 1.5;
  border-radius: 4px;
}
.toc a:hover { color: var(--fg); background: var(--bg-elev); }
.toc a.current {
  color: var(--accent);
  font-weight: 600;
  box-shadow: inset 2px 0 0 var(--accent);
  background: var(--accent-soft);
}

/* 掌握度圓點：5 顆，每顆 2 張卡 */
.dots { display: inline-flex; gap: 3px; flex: none; }
.dots i {
  width: 6px; height: 6px;
  border-radius: 50%;
  border: 1.5px solid var(--fg-faint);
}
.dots i.on { background: var(--accent); border-color: var(--accent); }

.progress-total {
  margin-top: auto;
  padding: 0.9rem 1.25rem 0 0;
  border-top: 1px solid var(--line);
  color: var(--fg-faint);
  font-size: 13px;
  font-variant-numeric: tabular-nums;
}

/* ---------------------------------------------------------------- 內容 */

main {
  margin-left: var(--side-w);
  padding: 3.5rem 3rem 6rem;
  max-width: calc(var(--side-w) + 78ch);
}

article { max-width: 68ch; }

h1 {
  font-size: 2rem;
  line-height: 1.3;
  letter-spacing: -0.02em;
  margin: 0 0 0.5rem;
}
h2 {
  font-size: 1.35rem;
  line-height: 1.4;
  margin: 3rem 0 0.75rem;
  padding-top: 0.5rem;
  letter-spacing: -0.01em;
}
h3 { font-size: 1.08rem; margin: 2rem 0 0.5rem; }
h4 { font-size: 1rem; margin: 1.5rem 0 0.4rem; color: var(--fg-dim); }

p { margin: 0 0 1.1rem; }

.source {
  color: var(--fg-faint);
  font-size: 14px;
  margin-bottom: 2.5rem;
  padding-bottom: 1.25rem;
  border-bottom: 1px solid var(--line);
}

ul, ol { margin: 0 0 1.1rem; padding-left: 1.4rem; }
li { margin: 0.3rem 0; }
li > ul, li > ol { margin: 0.3rem 0 0.5rem; }

blockquote {
  margin: 1.5rem 0;
  padding: 0.1rem 1.25rem;
  border-left: 3px solid var(--accent);
  background: var(--accent-soft);
  border-radius: 0 6px 6px 0;
  color: var(--fg-dim);
}

hr { border: 0; border-top: 1px solid var(--line); margin: 3rem 0; }

code {
  font-family: var(--mono);
  font-size: 0.88em;
  background: var(--code-bg);
  padding: 0.12em 0.38em;
  border-radius: 4px;
}

pre {
  background: var(--code-bg);
  border: 1px solid var(--line);
  border-radius: 8px;
  padding: 1rem 1.15rem;
  overflow-x: auto;
  margin: 0 0 1.4rem;
  line-height: 1.65;
}
pre code { background: none; padding: 0; font-size: 14px; }

/* 寬內容自己捲，body 永不橫捲 */
.table-wrap { overflow-x: auto; margin: 0 0 1.5rem; }
table { border-collapse: collapse; width: 100%; font-size: 15px; }
th, td {
  text-align: left;
  padding: 0.55rem 0.85rem;
  border-bottom: 1px solid var(--line);
  vertical-align: top;
}
th { font-weight: 600; color: var(--fg-dim); white-space: nowrap; }
tbody tr:last-child td { border-bottom: 0; }

.katex-display { overflow-x: auto; overflow-y: hidden; padding: 0.4rem 0; }

/* ------------------------------------------------------------- 上下頁 */

.pager {
  display: flex;
  justify-content: space-between;
  gap: 1rem;
  max-width: 68ch;
  margin-top: 4rem;
  padding-top: 1.5rem;
  border-top: 1px solid var(--line);
  font-size: 15px;
}
.pager a { text-decoration: none; color: var(--fg-dim); }
.pager a:hover { color: var(--accent); }
.pager .next { margin-left: auto; text-align: right; }

/* ------------------------------------------------------------ 手機版 */

#menu, #scrim { display: none; }

@media (max-width: 900px) {
  body { font-size: 16px; }

  #menu {
    display: block;
    position: fixed;
    top: 0.75rem; left: 0.75rem;
    z-index: 30;
    width: 40px; height: 40px;
    font-size: 18px;
    line-height: 1;
    background: var(--bg-elev);
    color: var(--fg);
    border: 1px solid var(--line);
    border-radius: 8px;
    cursor: pointer;
  }

  #side {
    z-index: 25;
    transform: translateX(-100%);
    transition: transform 0.2s ease;
    box-shadow: 0 0 40px rgb(0 0 0 / 0.18);
  }
  body.nav-open #side { transform: none; }

  body.nav-open #scrim {
    display: block;
    position: fixed;
    inset: 0;
    z-index: 20;
    background: rgb(0 0 0 / 0.4);
  }

  main {
    margin-left: 0;
    padding: 4.5rem 1.25rem 5rem;
    max-width: 100%;
  }
  article, .pager { max-width: 100%; }
}

@media (prefers-reduced-motion: reduce) {
  html { scroll-behavior: auto; }
  #side { transition: none; }
}

/* ============================================================ 互動元件
   引導式手算題（#5）與閃卡（#6）。狀態顏色另立 token，深淺色各一組。 */

:root {
  --ok: #0f766e;
  --ok-bg: #e3f2ef;
  --no: #b3411b;
  --no-bg: #fbeae4;
  --lock: #f3f1ed;
}
@media (prefers-color-scheme: dark) {
  :root {
    --ok: #5eead4;
    --ok-bg: #15332e;
    --no: #f0a08a;
    --no-bg: #3a201a;
    --lock: #16191e;
  }
}

.walkthrough, .cards { margin: 2.5rem 0; }

.wt-head h3, .cards-head h4 { margin: 0 0 0.35rem; }
.wt-head p, .cards-head p { color: var(--fg-dim); font-size: 15px; margin: 0 0 1.25rem; }

/* ---- 分段 */

.wt-part {
  border: 1px solid var(--line);
  border-radius: 10px;
  padding: 1.25rem 1.35rem;
  margin-bottom: 1.25rem;
  background: var(--bg-elev);
}
.wt-part.part-locked { opacity: 0.5; }
.wt-part.part-done { border-color: var(--ok); }

.wt-part-head h4 { margin: 0 0 0.3rem; font-size: 1.05rem; color: var(--fg); }
.wt-part-head p { margin: 0 0 1.1rem; color: var(--fg-dim); font-size: 15px; line-height: 1.7; }

/* ---- 單一步驟 */

.wt-step {
  border-top: 1px solid var(--line);
  padding: 1.1rem 0 0.9rem;
  position: relative;
}
.wt-step:first-of-type { border-top: 0; padding-top: 0.25rem; }

.wt-step.locked { opacity: 0.35; pointer-events: none; filter: grayscale(0.6); }
.wt-step.locked .wt-body::after {
  content: "先完成上一步";
  font-size: 13px;
  color: var(--fg-faint);
}
.wt-step.locked .wt-body > * { display: none; }

.wt-num {
  font-size: 12px;
  font-weight: 700;
  letter-spacing: 0.04em;
  color: var(--fg-faint);
  font-variant-numeric: tabular-nums;
  margin-bottom: 0.3rem;
}
.wt-num span { font-weight: 400; }
.wt-step.done .wt-num::after { content: " ✓"; color: var(--ok); }

.wt-prompt { margin-bottom: 0.8rem; line-height: 1.75; }

/* ---- 填空 */

.wt-fill {
  display: flex;
  flex-wrap: wrap;
  align-items: center;
  gap: 0.35rem;
  font-family: var(--mono);
  font-size: 15px;
  background: var(--code-bg);
  border-radius: 6px;
  padding: 0.7rem 0.85rem;
  margin-bottom: 0.7rem;
}
.wt-input {
  font: inherit;
  padding: 0.3rem 0.55rem;
  min-width: 8ch;
  border: 1px solid var(--accent);
  border-radius: 5px;
  background: var(--bg-elev);
  color: var(--fg);
}
.wt-input:focus { outline: 2px solid var(--accent); outline-offset: 1px; }
.wt-input:disabled { border-color: var(--ok); color: var(--ok); font-weight: 600; }

/* ---- 按鈕 */

.wt-btns { display: flex; gap: 0.5rem; }
.wt-btn {
  font: inherit;
  font-size: 14px;
  padding: 0.42rem 0.95rem;
  border-radius: 6px;
  border: 1px solid var(--line);
  background: var(--bg-elev);
  color: var(--fg);
  cursor: pointer;
}
.wt-btn:hover:not(:disabled) { border-color: var(--accent); color: var(--accent); }
.wt-btn:disabled { opacity: 0.45; cursor: default; }
.wt-btn.primary { background: var(--accent); border-color: var(--accent); color: var(--bg); font-weight: 600; }
.wt-btn.primary:hover:not(:disabled) { filter: brightness(1.08); color: var(--bg); }
.wt-btn.ghost { color: var(--fg-dim); }

/* ---- 選擇題 */

.wt-options { display: flex; flex-direction: column; gap: 0.45rem; }
.wt-opt {
  font: inherit;
  font-size: 15px;
  text-align: left;
  line-height: 1.6;
  padding: 0.6rem 0.9rem;
  border: 1px solid var(--line);
  border-radius: 7px;
  background: var(--bg);
  color: var(--fg);
  cursor: pointer;
}
.wt-opt:hover:not(:disabled) { border-color: var(--accent); background: var(--accent-soft); }
.wt-opt:disabled { cursor: default; }
.wt-opt.picked-ok { border-color: var(--ok); background: var(--ok-bg); font-weight: 600; }
.wt-opt.picked-no { border-color: var(--no); background: var(--no-bg); opacity: 0.75; text-decoration: line-through; }

/* ---- 回饋 */

.wt-feedback {
  margin-top: 0.75rem;
  padding: 0 0.9rem;
  border-radius: 7px;
  font-size: 15px;
  line-height: 1.7;
  max-height: 0;
  overflow: hidden;
  transition: max-height 0.15s ease, padding 0.15s ease;
}
.wt-feedback.ok, .wt-feedback.no, .wt-feedback.hint {
  max-height: 60rem;
  padding: 0.7rem 0.9rem;
}
.wt-feedback.ok { background: var(--ok-bg); border-left: 3px solid var(--ok); }
.wt-feedback.no { background: var(--no-bg); border-left: 3px solid var(--no); }
.wt-feedback.hint { background: var(--code-bg); border-left: 3px solid var(--fg-faint); }

.wt-error { color: var(--no); }

/* ---- 閃卡 */

.card {
  border: 1px solid var(--line);
  border-left: 3px solid var(--fg-faint);
  border-radius: 8px;
  padding: 1rem 1.15rem;
  margin-bottom: 0.9rem;
  background: var(--bg-elev);
}
.card[data-box="2"] { border-left-color: var(--accent); }
.card[data-box="3"] { border-left-color: var(--ok); }

.card-meta {
  display: flex;
  justify-content: space-between;
  gap: 1rem;
  font-size: 12px;
  color: var(--fg-faint);
  margin-bottom: 0.5rem;
}
.card-meta .kind {
  border: 1px solid var(--line);
  border-radius: 20px;
  padding: 0.05rem 0.55rem;
}
.card-front { line-height: 1.75; margin-bottom: 0.85rem; }

.card-back {
  display: none;
  border-top: 1px solid var(--line);
  padding-top: 0.85rem;
  margin-bottom: 0.85rem;
  line-height: 1.75;
  color: var(--fg-dim);
}
.card.revealed .card-back { display: block; }

.card-grade { display: none; gap: 0.5rem; }
.card.revealed .card-grade { display: flex; }
.card.graded .card-grade button { display: none; }

.grade-no:hover:not(:disabled)  { border-color: var(--no); color: var(--no); }
.grade-mid:hover:not(:disabled) { border-color: var(--fg-dim); color: var(--fg); }
.grade-ok:hover:not(:disabled)  { border-color: var(--ok); color: var(--ok); }

.card-grade .mastered { color: var(--ok); font-size: 14px; font-weight: 600; }
.card-grade .again { color: var(--fg-dim); font-size: 14px; }

@media (max-width: 600px) {
  .wt-part { padding: 1rem 0.9rem; }
  .wt-fill { font-size: 14px; }
}