:root {
  --bg: #fafafa;
  --fg: #222;
  --muted: rgba(60,60,60,0.6);
  --accent: #e74c3c;
  --green: #2ecc71;
  --purple: #6a4c93;
  --card-bg: #fff;
  --border: rgba(0,0,0,0.08);
  --hover: rgba(0,0,0,0.04);
}
@media (prefers-color-scheme: dark) {
  :root { --bg: #1a1a1a; --fg: #eee; --muted: rgba(220,220,220,0.55); --card-bg: #242424; --border: rgba(255,255,255,0.08); --hover: rgba(255,255,255,0.05); }
}
:root.light { --bg: #fafafa; --fg: #222; --muted: rgba(60,60,60,0.6); --card-bg: #fff; --border: rgba(0,0,0,0.08); --hover: rgba(0,0,0,0.04); }
:root.dark { --bg: #1a1a1a; --fg: #eee; --muted: rgba(220,220,220,0.55); --card-bg: #242424; --border: rgba(255,255,255,0.08); --hover: rgba(255,255,255,0.05); }

* { box-sizing: border-box; }
body { margin: 0; font-family: "Noto Sans CJK JP","Hiragino Sans",-apple-system,system-ui,sans-serif; background: var(--bg); color: var(--fg); }
.muted { color: var(--muted); }

header { display: flex; align-items: center; gap: 12px; padding: 10px 16px; border-bottom: 1px solid var(--border); position: sticky; top: 0; background: var(--bg); z-index: 10; }
header h1 { font-size: 18px; margin: 0; font-weight: 600; }
header h1 .muted { font-weight: 400; font-size: 14px; }
#search { flex: 1; padding: 8px 12px; border: 1px solid var(--border); border-radius: 8px; background: var(--card-bg); color: var(--fg); font-size: 15px; }
#menu-btn, #theme-btn { background: none; border: none; color: var(--fg); font-size: 22px; cursor: pointer; padding: 4px 8px; }

#layout { display: grid; grid-template-columns: 240px 1fr; min-height: calc(100vh - 90px); }
#sidebar { border-right: 1px solid var(--border); padding: 12px; overflow-y: auto; height: calc(100vh - 56px); position: sticky; top: 56px; }
#filters { display: flex; flex-direction: column; gap: 6px; margin-bottom: 14px; padding-bottom: 10px; border-bottom: 1px solid var(--border); font-size: 14px; }
#filters label { cursor: pointer; }
#lessons { list-style: none; padding: 0; margin: 0; }
#lessons li { padding: 8px 12px; border-radius: 6px; cursor: pointer; font-size: 14px; display: flex; justify-content: space-between; }
#lessons li:hover { background: var(--hover); }
#lessons li.active { background: var(--accent); color: #fff; font-weight: 500; }
#lessons li .count { opacity: 0.7; font-size: 12px; }

#content { padding: 20px; }
#intro { max-width: 720px; margin: 0 auto 24px; }
#cards { display: grid; grid-template-columns: repeat(auto-fill, minmax(280px, 1fr)); gap: 14px; max-width: 1400px; margin: 0 auto; }
#empty { text-align: center; padding: 60px 20px; color: var(--muted); font-size: 18px; }

.card { background: var(--card-bg); border: 1px solid var(--border); border-radius: 12px; padding: 16px; cursor: pointer; transition: transform 0.12s, box-shadow 0.12s; position: relative; min-height: 140px; }
.card:hover { transform: translateY(-1px); box-shadow: 0 4px 12px rgba(0,0,0,0.08); }
.card.learned { opacity: 0.55; }
.card .theme { position: absolute; top: 0; left: 0; right: 0; height: 4px; border-radius: 12px 12px 0 0; }
.card .lesson-tag { font-size: 11px; color: var(--muted); margin-bottom: 6px; }
.card .jp { font-size: 32px; font-weight: 600; margin: 4px 0; }
.card .kana { font-size: 18px; opacity: 0.8; margin: 4px 0; }
.card .pitch { display: inline-block; letter-spacing: 0.04em; }
.card .pitch .hi, .card .pitch .lo, .card .pitch .drop { display: inline-block; padding: 2px 1px 0; line-height: 1.1; }
.card .pitch .hi { border-top: 3px solid var(--accent); }
.card .pitch .lo { border-top: 3px solid transparent; }
.card .pitch .drop { border-right: 3px solid var(--accent); padding-right: 3px; }
.card .meaning { font-size: 15px; color: var(--green); margin-top: 6px; font-weight: 500; }
.card .meaning-secondary { font-size: 13px; color: #f39c12; margin-top: 2px; font-weight: 400; }
.card .actions { display: flex; gap: 8px; margin-top: 10px; align-items: center; }
.card .actions button { background: var(--hover); border: 1px solid var(--border); border-radius: 6px; padding: 4px 10px; cursor: pointer; color: var(--fg); font-size: 13px; }
.card .actions button:hover { background: var(--accent); color: #fff; border-color: var(--accent); }
.card .actions .learn { margin-left: auto; }
.card .actions .learn.on { background: var(--green); color: #fff; border-color: var(--green); }

/* expanded card */
.card.expanded { grid-column: 1 / -1; max-width: 720px; justify-self: center; min-height: auto; padding: 24px; }
.card.expanded .jp { font-size: 56px; }
.card.expanded .kana { font-size: 28px; }
.card.expanded .meaning { font-size: 20px; }
.card.expanded .sentence { margin: 16px 0; padding: 12px; background: var(--hover); border-radius: 8px; }
.card.expanded .sentence-jp { font-size: 20px; margin-bottom: 4px; }
.card.expanded .sentence-en { font-size: 14px; opacity: 0.7; font-style: italic; }
.card.expanded .mnemonic { font-style: italic; color: var(--purple); background: rgba(160,120,220,0.12); padding: 12px 16px; border-radius: 10px; margin: 14px 0; font-size: 15px; }
.card.expanded .mnemonic::before { content: "🧠 "; }
.card.expanded .kanji-svgs { display: flex; gap: 8px; justify-content: center; flex-wrap: wrap; margin: 12px 0; }
.card.expanded .kanji-svgs img { width: 120px; height: 120px; filter: invert(0); }
:root.dark .card.expanded .kanji-svgs img { filter: invert(1); }
@media (prefers-color-scheme: dark) { :root:not(.light) .card.expanded .kanji-svgs img { filter: invert(1); } }

footer { padding: 14px 16px; text-align: center; border-top: 1px solid var(--border); font-size: 13px; color: var(--muted); }
footer a { color: var(--accent); text-decoration: none; }

#intro h1 { margin: 0 0 6px; }
#intro .subtitle { color: var(--muted); margin-bottom: 18px; }
#intro img { display: block; max-width: 200px; margin: 0 auto 16px; border-radius: 8px; box-shadow: 0 4px 14px rgba(0,0,0,0.18); }
#intro h2 { font-size: 17px; margin: 18px 0 6px; border-bottom: 1px solid var(--border); padding-bottom: 3px; }
#intro ul { padding-left: 22px; }
#intro li { margin: 3px 0; }
#intro code { background: var(--hover); padding: 1px 6px; border-radius: 4px; font-size: 14px; }

@media (max-width: 720px) {
  #layout { grid-template-columns: 1fr; }
  #sidebar { position: fixed; left: -260px; top: 56px; width: 240px; background: var(--bg); transition: left 0.2s; z-index: 5; height: calc(100vh - 56px); }
  #sidebar.open { left: 0; }
  #menu-btn { display: inline-block; }
  #cards { grid-template-columns: 1fr; }
}
@media (min-width: 721px) { #menu-btn { display: none; } }