:root {
  --bg: #f7f5f0;
  --card: #ffffff;
  --border: #e0dbd0;
  --green: #3d6b52;
  --green-light: #e8f0eb;
  --text: #2a2a2a;
  --muted: #6b6b6b;
  --ok-bg: #dcfce7; --ok-border: #22c55e; --ok-text: #166534;
  --no-bg: #fee2e2; --no-border: #c0392b; --no-text: #991b1b;
  --yellow: #fef9c3;
  --yellow-border: #fde68a;
  --tip-strong: #92400e;
  --m-known: #3d6b52; --m-learning: #8fbfa0; --m-review: #c0392b; --m-new: #e4dfd5;
  font-size: 16px;
}
@media (prefers-color-scheme: dark) {
  :root {
    --bg: #1a1a1a;
    --card: #252525;
    --border: #3a3a3a;
    --green: #5a9e73;
    --green-light: #1e3028;
    --text: #e8e8e8;
    --muted: #a0a0a0;
    --ok-bg: #14321f; --ok-border: #22c55e; --ok-text: #86efac;
    --no-bg: #3a1717; --no-border: #e05a4b; --no-text: #fca5a5;
    --yellow: #3a3510;
    --yellow-border: #6b5d1a;
    --tip-strong: #fcd34d;
    --m-known: #7cc596; --m-learning: #356b4b; --m-review: #e86a5a; --m-new: #303030;
  }
}
* { box-sizing: border-box; margin: 0; padding: 0; }
body { background: var(--bg); color: var(--text); font-family: 'Segoe UI', system-ui, -apple-system, sans-serif; min-height: 100vh; }
button { font-family: inherit; }

.header { background: var(--green); color: white; padding: 16px 20px; }
.header h1 { font-size: 1.1rem; font-weight: 700; }
.header p { font-size: 0.8rem; opacity: 0.9; margin-top: 2px; }

/* Lesson picker */
.lesson-bar { display: flex; flex-wrap: wrap; gap: 6px; align-items: center; padding: 10px 16px; background: var(--card); border-bottom: 1px solid var(--border); }
.lb-spacer { flex: 1; }
.lb-label { font-size: 0.75rem; font-weight: 700; color: var(--muted); margin-right: 2px; }
.chip { font-size: 0.78rem; font-weight: 600; padding: 5px 11px; border-radius: 99px; border: 1.5px solid var(--border); background: var(--card); color: var(--muted); cursor: pointer; }
.chip.on { background: var(--green); border-color: var(--green); color: white; }
.chip-link { font-size: 0.75rem; background: none; border: none; color: var(--green); cursor: pointer; text-decoration: underline; }

.tabs { display: flex; background: var(--card); border-bottom: 2px solid var(--border); overflow-x: auto; }
.tab { padding: 10px 16px; font-size: 0.82rem; font-weight: 600; cursor: pointer; white-space: nowrap; border: none; border-bottom: 3px solid transparent; background: none; color: var(--muted); }
.tab.active { border-bottom-color: var(--green); color: var(--green); }

.content { padding: 16px; max-width: 680px; margin: 0 auto; }
.section { display: none; }
.section.active { display: block; }

/* Vocab list */
.lesson-label { font-size: 0.7rem; font-weight: 700; text-transform: uppercase; letter-spacing: 0.08em; color: var(--green); margin: 18px 0 8px; }
.vocab-grid { display: grid; gap: 8px; }
.vocab-card { background: var(--card); border: 1px solid var(--border); border-radius: 10px; padding: 12px 14px; display: flex; justify-content: space-between; align-items: center; gap: 10px; cursor: pointer; }
.vocab-card:hover { background: var(--green-light); }
.vocab-korean { font-size: 1.2rem; font-weight: 600; }
.vocab-english { font-size: 0.85rem; color: var(--muted); }
.vocab-note { font-size: 0.72rem; color: var(--muted); font-style: italic; }
.vocab-tag { font-size: 0.65rem; background: var(--green-light); color: var(--green); padding: 2px 7px; border-radius: 99px; font-weight: 600; }
.vocab-card.flipped .vocab-english { color: var(--text); font-weight: 500; }
.hide-en .vocab-card:not(.flipped) .vocab-english,
.hide-en .vocab-card:not(.flipped) .vocab-note { visibility: hidden; }
.toolbar { display: flex; gap: 8px; flex-wrap: wrap; align-items: center; margin-bottom: 4px; }

/* Flashcards */
.flash-wrap { perspective: 900px; margin: 20px auto; max-width: 400px; }
.flash-inner { position: relative; width: 100%; padding-bottom: 60%; transition: transform 0.5s; transform-style: preserve-3d; cursor: pointer; }
.flash-inner.flipped { transform: rotateY(180deg); }
.flash-face { position: absolute; inset: 0; background: var(--card); border: 2px solid var(--border); border-radius: 16px; display: flex; flex-direction: column; align-items: center; justify-content: center; padding: 20px; backface-visibility: hidden; -webkit-backface-visibility: hidden; text-align: center; }
.flash-back { transform: rotateY(180deg); }
.flash-main { font-size: 2rem; font-weight: 700; }
.flash-main.en { font-size: 1.35rem; }
.flash-pos { font-size: 0.7rem; color: var(--green); font-weight: 600; text-transform: uppercase; margin-top: 6px; }
.flash-note { font-size: 0.78rem; color: var(--muted); margin-top: 6px; }
.flash-controls { display: flex; gap: 10px; justify-content: center; margin-top: 14px; flex-wrap: wrap; }
.flash-progress { text-align: center; font-size: 0.8rem; color: var(--muted); margin-top: 8px; }
.kbd-hint { text-align: center; font-size: 0.72rem; color: var(--muted); margin-top: 10px; }

.btn { padding: 9px 20px; border-radius: 8px; border: none; font-size: 0.85rem; font-weight: 600; cursor: pointer; }
.btn-green { background: var(--green); color: white; }
.btn-outline { background: var(--card); color: var(--text); border: 1px solid var(--border); }
.btn-outline.on { border-color: var(--green); color: var(--green); background: var(--green-light); }
.btn:hover { opacity: 0.85; }
.btn-small { padding: 6px 12px; font-size: 0.78rem; }

/* Quiz */
.mode-grid { display: grid; gap: 10px; margin-top: 8px; }
.mode-card { background: var(--card); border: 1.5px solid var(--border); border-radius: 12px; padding: 14px 16px; cursor: pointer; text-align: left; color: var(--text); }
.mode-card:hover { border-color: var(--green); background: var(--green-light); }
.mode-card strong { display: block; font-size: 0.95rem; margin-bottom: 3px; }
.mode-card span { font-size: 0.8rem; color: var(--muted); }
.quiz-card { background: var(--card); border: 1px solid var(--border); border-radius: 12px; padding: 18px; margin-bottom: 14px; }
.quiz-q { font-size: 1rem; font-weight: 600; margin-bottom: 14px; line-height: 1.5; }
.quiz-korean { font-size: 1.4rem; }
.options { display: grid; gap: 8px; }
.opt { padding: 10px 14px; border: 1.5px solid var(--border); border-radius: 8px; cursor: pointer; font-size: 0.95rem; background: var(--card); color: var(--text); text-align: left; }
.opt:hover:not(:disabled) { border-color: var(--green); background: var(--green-light); }
.opt.correct { border-color: var(--ok-border); background: var(--ok-bg); color: var(--ok-text); }
.opt.wrong { border-color: var(--no-border); background: var(--no-bg); color: var(--no-text); }
.opt:disabled { cursor: default; }
.feedback { margin-top: 10px; font-size: 0.85rem; padding: 8px 12px; border-radius: 7px; line-height: 1.45; }
.feedback.ok { background: var(--ok-bg); color: var(--ok-text); border: 1px solid var(--ok-border); }
.feedback.no { background: var(--no-bg); color: var(--no-text); border: 1px solid var(--no-border); }
.quiz-score { text-align: center; padding: 24px 0; }
.score-big { font-size: 3rem; font-weight: 800; color: var(--green); }
.quiz-nav { display: flex; justify-content: space-between; align-items: center; margin-top: 14px; }
.meta { font-size: 0.75rem; color: var(--muted); margin-bottom: 6px; }
.missed { text-align: left; margin-top: 18px; background: var(--card); border: 1px solid var(--border); border-radius: 12px; padding: 12px 14px; }
.missed h3 { font-size: 0.8rem; text-transform: uppercase; letter-spacing: 0.06em; color: var(--no-text); margin-bottom: 8px; }
.missed li { font-size: 0.85rem; margin: 0 0 6px 18px; line-height: 1.45; }

/* Grammar */
.grammar-block { background: var(--card); border: 1px solid var(--border); border-radius: 12px; padding: 16px; margin-bottom: 12px; }
.grammar-title { font-size: 0.75rem; font-weight: 700; text-transform: uppercase; letter-spacing: 0.06em; color: var(--green); margin-bottom: 8px; }
.grammar-h { font-size: 1rem; font-weight: 700; margin-bottom: 6px; }
.grammar-h em { color: var(--green); font-style: normal; }
.grammar-body { font-size: 0.88rem; color: var(--muted); line-height: 1.55; }
.grammar-body .ko, .grammar-body strong { color: var(--text); }
.grammar-body .ko { font-weight: 600; }
.example-box { background: var(--green-light); border-left: 3px solid var(--green); border-radius: 6px; padding: 10px 12px; margin-top: 10px; font-size: 0.9rem; }
.example-box p { margin-bottom: 4px; }
.example-box b { color: var(--green); }
.rule-table { width: 100%; border-collapse: collapse; margin-top: 10px; font-size: 0.85rem; }
.rule-table th { background: var(--green); color: white; padding: 5px 10px; text-align: left; }
.rule-table td { border: 1px solid var(--border); padding: 5px 10px; }
.rule-table tr:nth-child(even) td { background: var(--green-light); }

.tip { background: var(--yellow); border: 1px solid var(--yellow-border); border-radius: 10px; padding: 12px 14px; margin-bottom: 14px; font-size: 0.85rem; line-height: 1.5; }
.tip strong { color: var(--tip-strong); }

/* Fill-in */
.blank-q { background: var(--card); border: 1px solid var(--border); border-radius: 10px; padding: 14px; margin-bottom: 10px; }
.blank-sentence { font-size: 1.1rem; margin-bottom: 12px; line-height: 2; }
.blank-input { border: 2px solid var(--border); border-radius: 7px; padding: 6px 10px; font-size: 1rem; width: 120px; font-family: inherit; background: var(--bg); color: var(--text); }
.blank-input.wide { width: 200px; }
.blank-input.correct { border-color: var(--ok-border); background: var(--ok-bg); color: var(--ok-text); }
.blank-input.wrong { border-color: var(--no-border); background: var(--no-bg); color: var(--no-text); }
.check-btn { padding: 6px 12px; background: var(--green); color: white; border: none; border-radius: 7px; cursor: pointer; font-size: 0.82rem; font-weight: 600; }
.check-btn.ghost { background: var(--card); color: var(--muted); border: 1px solid var(--border); }
.hint { margin-top: 8px; font-size: 0.8rem; color: var(--muted); }

/* Reference */
.speak-btn { background: none; border: 1.5px solid var(--green); color: var(--green); border-radius: 7px; padding: 3px 9px; font-size: 0.82rem; cursor: pointer; flex-shrink: 0; }
.speak-btn:hover { background: var(--green-light); }
.num-card { background: var(--card); border: 1px solid var(--border); border-radius: 10px; padding: 12px 14px; display: flex; align-items: center; justify-content: space-between; }
.num-digit { font-size: 1.6rem; font-weight: 800; color: var(--green); min-width: 36px; }
.num-ko { font-size: 1.5rem; font-weight: 700; margin-left: 10px; flex: 1; }
.num-rom { font-size: 0.78rem; color: var(--muted); margin: 0 8px; }
.phone-card { background: var(--card); border: 1px solid var(--border); border-radius: 10px; padding: 12px 14px; display: flex; align-items: center; justify-content: space-between; gap: 10px; }
.phone-num { font-size: 1.1rem; font-weight: 700; flex: 1; }
.phone-ko { font-size: 0.9rem; color: var(--muted); flex: 1.4; }
.reveal-on-tap { filter: blur(5px); cursor: pointer; transition: filter 0.2s; }
.reveal-on-tap.shown { filter: none; }

footer { text-align: center; font-size: 0.72rem; color: var(--muted); padding: 24px 16px 40px; }


/* Progress */
.review-card { border-color: var(--m-review); }
.tiles { display: grid; grid-template-columns: repeat(auto-fit, minmax(140px, 1fr)); gap: 10px; margin-bottom: 12px; }
.tile { background: var(--card); border: 1px solid var(--border); border-radius: 12px; padding: 12px 14px; }
.tile-num { font-size: 1.8rem; font-weight: 800; color: var(--text); line-height: 1.1; }
.tile-of { font-size: 1rem; color: var(--muted); font-weight: 600; }
.tile-label { font-size: 0.78rem; color: var(--muted); margin-top: 2px; line-height: 1.4; }
.up { color: var(--ok-text); font-weight: 600; }
.down { color: var(--no-text); font-weight: 600; }
.chart { width: 100%; height: auto; display: block; }
.chart .grid { stroke: var(--border); stroke-width: 1; }
.chart .axis { fill: var(--muted); font-size: 12px; }
.chart .val { fill: var(--text); font-size: 13px; font-weight: 700; }
.chart .line { fill: none; stroke: var(--green); stroke-width: 2; stroke-linejoin: round; stroke-linecap: round; }
.chart .dot { fill: var(--green); stroke: var(--card); stroke-width: 2; }
.chart .hit { fill: transparent; cursor: pointer; }
.chart .pt:hover .dot { r: 6.5; }
.legend { display: flex; flex-wrap: wrap; gap: 6px 14px; font-size: 0.78rem; color: var(--muted); margin: 10px 0 2px; }
.legend i { display: inline-block; width: 12px; height: 12px; border-radius: 3px; margin-right: 5px; vertical-align: -2px; }
.mrow { display: grid; grid-template-columns: 170px 1fr; gap: 4px 12px; align-items: center; margin: 8px 0; }
.mname { font-size: 0.85rem; }
.mcount { grid-column: 2; font-size: 0.75rem; color: var(--muted); }
.mbar { display: flex; gap: 2px; height: 12px; border-radius: 4px; overflow: hidden; }
.seg { display: block; min-width: 3px; }
.seg-known { background: var(--m-known); } .seg-learning { background: var(--m-learning); }
.seg-review { background: var(--m-review); } .seg-new { background: var(--m-new); }
.trouble { margin: 0 0 10px 18px; font-size: 0.88rem; line-height: 1.5; }
.trouble li { margin-bottom: 6px; }
details.hint summary { cursor: pointer; }
@media (max-width: 480px) { .mrow { grid-template-columns: 1fr; } .mcount { grid-column: 1; } }