/*
  Design concept: 田字格 practice-sheet / exam-booklet.
  Paper + ink neutrals, a cinnabar-seal red used like a teacher's marking pen
  or a stamp of authentication, jade green reserved for "correct/known".
  Hanzi set in a CJK serif (printed textbook), pinyin in monospace
  (typewritten romanization table), meanings in a plain text serif,
  UI chrome in a quiet sans.
*/

:root {
  --paper: #eae6db;
  --paper-raised: #f7f4ea;
  --ink: #2b2622;
  --ink-muted: #7a7060;
  --rule: #cfc5ac;
  --grid-line: rgba(43, 38, 34, 0.055);
  --seal: #a3392a;
  --seal-soft: #ecdad2;
  --jade: #3f6e54;
  --jade-soft: #dfe9de;
  --accent: var(--seal);
  --radius-sm: 4px;
  --radius-md: 6px;

  --font-hanzi: "Noto Serif SC", "Songti SC", "STSong", "SimSun", serif;
  --font-serif: Georgia, "Iowan Old Style", "Palatino Linotype", "Noto Serif", serif;
  --font-mono: ui-monospace, "SF Mono", "Cascadia Code", "Courier New", monospace;
  --font-sans: -apple-system, BlinkMacSystemFont, "Segoe UI", Roboto, "PingFang SC", Arial, sans-serif;
}

@media (prefers-color-scheme: dark) {
  :root {
    --paper: #1c1a16;
    --paper-raised: #262319;
    --ink: #ece5d4;
    --ink-muted: #a49a86;
    --rule: #3c3728;
    --grid-line: rgba(236, 229, 212, 0.045);
    --seal: #d97a56;
    --seal-soft: #3a2a20;
    --jade: #7fb894;
    --jade-soft: #223228;
  }
}
:root[data-theme="dark"] {
  --paper: #1c1a16;
  --paper-raised: #262319;
  --ink: #ece5d4;
  --ink-muted: #a49a86;
  --rule: #3c3728;
  --grid-line: rgba(236, 229, 212, 0.045);
  --seal: #d97a56;
  --seal-soft: #3a2a20;
  --jade: #7fb894;
  --jade-soft: #223228;
}
:root[data-theme="light"] {
  --paper: #eae6db;
  --paper-raised: #f7f4ea;
  --ink: #2b2622;
  --ink-muted: #7a7060;
  --rule: #cfc5ac;
  --grid-line: rgba(43, 38, 34, 0.055);
  --seal: #a3392a;
  --seal-soft: #ecdad2;
  --jade: #3f6e54;
  --jade-soft: #dfe9de;
}

* { box-sizing: border-box; }

html, body {
  margin: 0;
  padding: 0;
  background: var(--paper);
  color: var(--ink);
  font-family: var(--font-sans);
}

body {
  overflow-x: hidden;
  background-image:
    repeating-linear-gradient(var(--grid-line) 0 1px, transparent 1px 32px),
    repeating-linear-gradient(90deg, var(--grid-line) 0 1px, transparent 1px 32px);
}

::selection { background: var(--seal-soft); color: var(--seal); }

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

/* ---- Header ---- */
.topbar {
  display: flex;
  flex-direction: column;
  gap: 14px;
  padding: 20px 24px 0;
  background: var(--paper);
  border-bottom: 1px solid var(--rule);
  position: sticky;
  top: 0;
  z-index: 10;
}

.topbar-row {
  display: flex;
  align-items: baseline;
  justify-content: space-between;
  flex-wrap: wrap;
  gap: 12px;
}

.brand {
  font-family: var(--font-hanzi);
  font-size: 1.7rem;
  font-weight: 700;
  color: var(--ink);
  display: flex;
  align-items: baseline;
  gap: 12px;
}
.brand span {
  font-family: var(--font-mono);
  font-size: 0.66rem;
  font-weight: 600;
  text-transform: uppercase;
  letter-spacing: 0.1em;
  color: var(--ink-muted);
}

.level-switch {
  display: flex;
  gap: 3px;
  border: 1px solid var(--rule);
  border-radius: var(--radius-md);
  padding: 3px;
}
.level-btn {
  border: none;
  background: transparent;
  color: var(--ink-muted);
  font-family: var(--font-mono);
  font-size: 0.7rem;
  font-weight: 700;
  text-transform: uppercase;
  letter-spacing: 0.04em;
  padding: 7px 12px;
  border-radius: 3px;
  cursor: pointer;
}
.level-btn:hover { color: var(--ink); }
.level-btn.active { background: var(--seal); color: var(--paper-raised); }

.tabs {
  display: flex;
  gap: 28px;
  padding-top: 2px;
}
.tab-btn {
  border: none;
  background: none;
  color: var(--ink-muted);
  font-family: var(--font-sans);
  font-size: 0.86rem;
  font-weight: 600;
  padding: 10px 1px;
  margin-bottom: -1px;
  border-bottom: 2px solid transparent;
  cursor: pointer;
}
.tab-btn:hover { color: var(--ink); }
.tab-btn.active { color: var(--seal); border-bottom-color: var(--seal); }

#app {
  max-width: 900px;
  margin: 0 auto;
  padding: 24px 24px 20px;
}

.view { display: none; }
.view.active { display: block; }

.count-badge {
  font-family: var(--font-mono);
  font-size: 0.8rem;
  color: var(--ink-muted);
  font-weight: 600;
}

/* ---- List view ---- */
.list-toolbar {
  display: flex;
  align-items: center;
  gap: 14px;
  margin-bottom: 6px;
}
#searchBox {
  flex: 1;
  padding: 11px 14px;
  border-radius: var(--radius-sm);
  border: 1px solid var(--rule);
  background: var(--paper-raised);
  color: var(--ink);
  font-size: 0.95rem;
}
#searchBox::placeholder { color: var(--ink-muted); }
#searchBox:focus { outline: 2px solid var(--seal); outline-offset: -1px; }

.word-list {
  display: flex;
  flex-direction: column;
}

.word-card {
  border-bottom: 1px solid var(--rule);
  padding: 13px 4px;
  cursor: pointer;
}
.word-card:hover { background: var(--grid-line); }

.word-card-row {
  display: flex;
  align-items: baseline;
  gap: 12px;
  flex-wrap: wrap;
}

.word-hanzi { font-family: var(--font-hanzi); font-size: 1.4rem; font-weight: 700; }
.word-pinyin { font-family: var(--font-mono); color: var(--seal); font-weight: 600; font-size: 0.88rem; }
.word-pos {
  font-family: var(--font-mono);
  font-size: 0.66rem;
  text-transform: uppercase;
  letter-spacing: 0.04em;
  color: var(--ink-muted);
  border: 1px solid var(--rule);
  padding: 1px 6px;
  border-radius: 3px;
}
.word-meaning { font-family: var(--font-serif); color: var(--ink-muted); font-size: 0.92rem; margin-left: auto; }
.word-level-tag {
  font-family: var(--font-mono);
  font-size: 0.64rem;
  font-weight: 700;
  letter-spacing: 0.03em;
  color: var(--seal);
  border: 1px solid var(--seal);
  padding: 1px 6px;
  border-radius: 3px;
}

.word-example {
  display: none;
  margin-top: 10px;
  padding-top: 10px;
  border-top: 1px dashed var(--rule);
  font-family: var(--font-serif);
  font-size: 0.88rem;
  color: var(--ink-muted);
  line-height: 1.55;
}
.word-card.expanded .word-example { display: block; }
.word-example b { font-family: var(--font-hanzi); color: var(--ink); font-size: 1rem; }

.empty-state {
  text-align: center;
  padding: 40px 20px;
  color: var(--ink-muted);
  font-family: var(--font-serif);
}

/* ---- Flashcard view ---- */
.fc-toolbar {
  display: flex;
  justify-content: space-between;
  align-items: center;
  margin-bottom: 18px;
  flex-wrap: wrap;
  gap: 10px;
}
.fc-actions { display: flex; gap: 8px; }

.btn-secondary {
  border: 1px solid var(--rule);
  background: var(--paper-raised);
  color: var(--ink);
  padding: 8px 14px;
  border-radius: var(--radius-sm);
  font-family: var(--font-mono);
  font-size: 0.76rem;
  font-weight: 600;
  text-transform: uppercase;
  letter-spacing: 0.03em;
  cursor: pointer;
}
.btn-secondary:hover { border-color: var(--seal); color: var(--seal); }

.fc-stage {
  display: flex;
  align-items: center;
  justify-content: center;
  gap: 14px;
}

.fc-nav {
  border: 1px solid var(--rule);
  background: var(--paper-raised);
  color: var(--ink);
  width: 42px;
  height: 42px;
  border-radius: 50%;
  font-size: 1.3rem;
  cursor: pointer;
  flex-shrink: 0;
}
.fc-nav:hover { border-color: var(--seal); color: var(--seal); }
.fc-nav:disabled { opacity: 0.35; cursor: default; }

.flashcard {
  width: 100%;
  max-width: 460px;
  height: 320px;
  perspective: 1200px;
  cursor: pointer;
}
.flashcard-inner {
  position: relative;
  width: 100%;
  height: 100%;
  transition: transform 0.5s;
  transform-style: preserve-3d;
}
.flashcard.flipped .flashcard-inner { transform: rotateY(180deg); }

.flashcard-face {
  position: absolute;
  inset: 0;
  backface-visibility: hidden;
  border-radius: var(--radius-md);
  border: 1px solid var(--rule);
  background: var(--paper-raised);
  display: flex;
  flex-direction: column;
  align-items: center;
  justify-content: center;
  padding: 24px;
  text-align: center;
}
/* 田字格 practice-grid guide lines behind the character */
.flashcard-front::before {
  content: "";
  position: absolute;
  inset: 18%;
  background:
    linear-gradient(var(--rule), var(--rule)) center / 100% 1px no-repeat,
    linear-gradient(var(--rule), var(--rule)) center / 1px 100% no-repeat;
  opacity: 0.55;
  pointer-events: none;
}

.flashcard-back { transform: rotateY(180deg); justify-content: flex-start; padding-top: 40px; }

.fc-hanzi { position: relative; font-family: var(--font-hanzi); font-size: 4rem; font-weight: 700; line-height: 1; margin-bottom: 14px; }
.fc-pinyin { position: relative; font-family: var(--font-mono); font-size: 1.25rem; color: var(--seal); font-weight: 600; }
.fc-hint { position: absolute; bottom: 18px; font-family: var(--font-mono); font-size: 0.7rem; text-transform: uppercase; letter-spacing: 0.05em; color: var(--ink-muted); }

.fc-meaning { margin-bottom: 20px; }
.fc-vn { font-family: var(--font-serif); font-size: 1.5rem; font-weight: 700; }
.fc-en { font-family: var(--font-sans); font-size: 0.95rem; color: var(--ink-muted); margin-top: 4px; }

.fc-example {
  font-family: var(--font-serif);
  font-size: 0.9rem;
  line-height: 1.6;
  color: var(--ink-muted);
  border-top: 1px dashed var(--rule);
  padding-top: 14px;
  width: 100%;
}
.fc-example .ex-hanzi { font-family: var(--font-hanzi); color: var(--ink); font-size: 1.05rem; font-weight: 600; }
.fc-example .ex-pinyin { font-family: var(--font-mono); color: var(--seal); }

.fc-controls {
  display: flex;
  justify-content: center;
  gap: 14px;
  margin-top: 24px;
}
.btn-known, .btn-unknown {
  background: none;
  padding: 10px 20px;
  border-radius: var(--radius-sm);
  font-family: var(--font-mono);
  font-size: 0.76rem;
  font-weight: 700;
  text-transform: uppercase;
  letter-spacing: 0.04em;
  cursor: pointer;
}
.btn-known { border: 1.5px solid var(--jade); color: var(--jade); }
.btn-unknown { border: 1.5px solid var(--seal); color: var(--seal); }
.btn-known:hover { background: var(--jade-soft); }
.btn-unknown:hover { background: var(--seal-soft); }

/* ---- Quiz / fill-in shared stage ---- */
.quiz-toolbar {
  display: flex;
  justify-content: space-between;
  align-items: center;
  margin-bottom: 18px;
}

.quiz-stage {
  display: flex;
  flex-direction: column;
  align-items: center;
  gap: 22px;
}

.quiz-question {
  background: var(--paper-raised);
  border: 1px solid var(--rule);
  border-radius: var(--radius-md);
  padding: 32px;
  width: 100%;
  max-width: 460px;
  text-align: center;
}
.quiz-hanzi { font-family: var(--font-hanzi); font-size: 3rem; font-weight: 700; }
.quiz-pinyin { font-family: var(--font-mono); color: var(--seal); font-weight: 600; margin-top: 6px; }
.fill-prompt { font-family: var(--font-serif); font-size: 1.9rem; font-weight: 700; text-wrap: balance; }

.quiz-options {
  display: grid;
  grid-template-columns: 1fr 1fr;
  gap: 10px;
  width: 100%;
  max-width: 460px;
}
.quiz-option {
  border: 1px solid var(--rule);
  background: var(--paper-raised);
  color: var(--ink);
  font-family: var(--font-serif);
  padding: 14px 12px;
  border-radius: var(--radius-sm);
  font-size: 0.92rem;
  cursor: pointer;
  text-align: center;
}
.quiz-option:hover { border-color: var(--seal); }
.quiz-option.correct { background: var(--jade-soft); border-color: var(--jade); color: var(--jade); }
.quiz-option.correct::before { content: "✓ "; }
.quiz-option.wrong { background: var(--seal-soft); border-color: var(--seal); color: var(--seal); }
.quiz-option.wrong::before { content: "✗ "; }
.quiz-option:disabled { cursor: default; }

.quiz-next {
  border: 1.5px solid var(--seal);
  background: none;
  color: var(--seal);
  padding: 11px 24px;
  border-radius: var(--radius-sm);
  font-family: var(--font-mono);
  font-size: 0.8rem;
  font-weight: 700;
  text-transform: uppercase;
  letter-spacing: 0.04em;
  cursor: pointer;
  visibility: hidden;
}
.quiz-next:hover { background: var(--seal-soft); }
.quiz-next.show { visibility: visible; }

.quiz-done { text-align: center; padding: 40px 20px; }
.quiz-done .score-big { font-family: var(--font-hanzi); font-size: 2.6rem; font-weight: 800; color: var(--seal); }
.quiz-done p { font-family: var(--font-serif); color: var(--ink-muted); }

/* ---- Fill-in-the-blank view ---- */
.fill-question { font-family: var(--font-sans); color: var(--ink-muted); font-size: 0.9rem; margin-top: 10px; }
.fill-form {
  display: flex;
  gap: 10px;
  width: 100%;
  max-width: 460px;
}
.fill-input {
  flex: 1;
  padding: 13px 16px;
  border-radius: var(--radius-sm);
  border: 1px solid var(--rule);
  background: var(--paper-raised);
  color: var(--ink);
  font-family: var(--font-mono);
  font-size: 1rem;
}
.fill-input::placeholder { color: var(--ink-muted); font-family: var(--font-sans); }
.fill-input:focus { outline: 2px solid var(--seal); outline-offset: -1px; }
.fill-input.correct { border-color: var(--jade); background: var(--jade-soft); color: var(--jade); }
.fill-input.wrong { border-color: var(--seal); background: var(--seal-soft); color: var(--seal); }
.fill-submit {
  border: 1.5px solid var(--seal);
  background: var(--seal);
  color: var(--paper-raised);
  padding: 0 22px;
  border-radius: var(--radius-sm);
  font-family: var(--font-mono);
  font-size: 0.8rem;
  font-weight: 700;
  text-transform: uppercase;
  letter-spacing: 0.04em;
  cursor: pointer;
}
.fill-submit:disabled { opacity: 0.5; cursor: default; }
.fill-feedback {
  width: 100%;
  max-width: 460px;
  font-family: var(--font-serif);
  font-size: 0.92rem;
  text-align: center;
  min-height: 1.4em;
}
.fill-feedback .correct-answer { font-family: var(--font-hanzi); color: var(--jade); font-weight: 700; }

.footer {
  text-align: center;
  font-family: var(--font-mono);
  color: var(--ink-muted);
  font-size: 0.72rem;
  text-transform: uppercase;
  letter-spacing: 0.06em;
  padding: 34px 20px 44px;
}

@media (max-width: 560px) {
  .quiz-options { grid-template-columns: 1fr; }
  .flashcard { height: 360px; }
  .word-meaning { margin-left: 0; width: 100%; }
}