:root {
  --bg: #f4f1ea;
  --panel: #ffffff;
  --text: #1f2430;
  --text-dim: #6b7280;
  --border: #d8d3c6;
  --border-strong: #35302a;
  --accent: #b5563a;
  --on-accent: #fff9f2;
  --accent-2: #3d6b5c;
  --cell-bg: #ffffff;
  --cell-given: #eae5d8;
  --cell-selected: #f2d9c6;
  --cell-peer: #f6efe4;
  --cell-same: #dcecdf;
  --cell-error: #f6d3ce;
  --cell-error-text: #b5563a;
  --notes: #9a927f;
  --shadow: rgba(31, 36, 48, 0.08);
  --btn-bg: #ffffff;
  --btn-bg-hover: #f0ece1;
}
@media (prefers-color-scheme: dark) {
  :root:not([data-theme="light"]) {
    --bg: #1b1a17;
    --panel: #242320;
    --text: #ece7db;
    --text-dim: #a39c8c;
    --border: #5c574c;
    --border-strong: #ece7db;
    --accent: #d97a58;
    --on-accent: #1b1a17;
    --accent-2: #8fd0b4;
    --cell-bg: #242320;
    --cell-given: #3a372f;
    --cell-selected: #6a4a33;
    --cell-peer: #33312b;
    --cell-same: #2f5a45;
    --cell-error: #5a2a26;
    --cell-error-text: #ff9a85;
    --notes: #d2ccbb;
    --shadow: rgba(0, 0, 0, 0.35);
    --btn-bg: #2d2b26;
    --btn-bg-hover: #383530;
  }
}
:root[data-theme="dark"] {
  --bg: #1b1a17;
  --panel: #242320;
  --text: #ece7db;
  --text-dim: #a39c8c;
  --border: #5c574c;
  --border-strong: #ece7db;
  --accent: #d97a58;
  --on-accent: #1b1a17;
  --accent-2: #8fd0b4;
  --cell-bg: #242320;
  --cell-given: #3a372f;
  --cell-selected: #6a4a33;
  --cell-peer: #33312b;
  --cell-same: #2f5a45;
  --cell-error: #5a2a26;
  --cell-error-text: #ff9a85;
  --notes: #d2ccbb;
  --shadow: rgba(0, 0, 0, 0.35);
  --btn-bg: #2d2b26;
  --btn-bg-hover: #383530;
}

* { box-sizing: border-box; }
html, body {
  margin: 0;
  padding: 0;
  background: var(--bg);
  color: var(--text);
  font-family: 'Iowan Old Style', 'Georgia', 'Charter', serif;
}
body {
  min-height: 100vh;
  display: flex;
  justify-content: center;
  padding: 24px 14px 40px;
}
.app {
  width: 100%;
  max-width: 560px;
  display: flex;
  flex-direction: column;
  align-items: center;
  gap: 16px;
}
h1 {
  font-size: 1.6rem;
  letter-spacing: 0.04em;
  margin: 4px 0 0;
  font-weight: 600;
}
.subtitle {
  color: var(--text-dim);
  font-size: 0.85rem;
  margin-top: -10px;
  text-align: center;
}

.difficulty-bar {
  display: flex;
  gap: 8px;
  flex-wrap: wrap;
  justify-content: center;
}
.diff-btn {
  font-family: inherit;
  padding: 7px 16px;
  border-radius: 999px;
  border: 1px solid var(--border);
  background: var(--btn-bg);
  color: var(--text);
  cursor: pointer;
  font-size: 0.85rem;
  transition: background 0.15s ease, border-color 0.15s ease;
}
.diff-btn:hover { background: var(--btn-bg-hover); }
.diff-btn.active {
  background: var(--accent);
  border-color: var(--accent);
  color: var(--on-accent);
}

.status-row {
  display: flex;
  justify-content: space-between;
  align-items: center;
  width: 100%;
  max-width: 460px;
  font-size: 0.85rem;
  color: var(--text-dim);
  padding: 0 2px;
}
.status-row span.value { color: var(--text); font-variant-numeric: tabular-nums; }

.board-wrap {
  width: 100%;
  max-width: 460px;
  aspect-ratio: 1 / 1;
  background: var(--panel);
  border-radius: 10px;
  box-shadow: 0 6px 18px var(--shadow);
  padding: 10px;
  position: relative;
}
.board {
  display: grid;
  grid-template-columns: repeat(9, 1fr);
  grid-template-rows: repeat(9, 1fr);
  width: 100%;
  height: 100%;
  border: 2px solid var(--border-strong);
  border-radius: 4px;
  overflow: hidden;
}
.cell {
  position: relative;
  display: flex;
  align-items: center;
  justify-content: center;
  background: var(--cell-bg);
  border: 1px solid var(--border);
  cursor: pointer;
  font-size: clamp(1rem, 3.6vw, 1.4rem);
  color: var(--text);
  user-select: none;
  transition: background 0.1s ease;
}
.cell.given { background: var(--cell-given); font-weight: 600; cursor: default; }
.cell.peer { background: var(--cell-peer); }
.cell.same-num { background: var(--cell-same); }
.cell.selected { background: var(--cell-selected); }
.cell.error { background: var(--cell-error); color: var(--cell-error-text); }
.cell:nth-child(3n) { border-right: 2px solid var(--border-strong); }
.cell:nth-child(9n+1) { border-left: 2px solid var(--border-strong); }
.row-thick-top { border-top: 2px solid var(--border-strong) !important; }

.notes-grid {
  position: absolute;
  inset: 3px;
  display: grid;
  grid-template-columns: repeat(3, 1fr);
  grid-template-rows: repeat(3, 1fr);
  pointer-events: none;
}
.notes-grid span {
  display: flex;
  align-items: center;
  justify-content: center;
  font-size: 0.62rem;
  color: var(--notes);
}

.controls {
  display: flex;
  flex-direction: column;
  gap: 12px;
  width: 100%;
  max-width: 460px;
  align-items: center;
}
.numpad {
  display: grid;
  grid-template-columns: repeat(9, 1fr);
  gap: 6px;
  width: 100%;
}
.num-btn {
  font-family: inherit;
  aspect-ratio: 1 / 1;
  border-radius: 8px;
  border: 1px solid var(--border);
  background: var(--btn-bg);
  color: var(--text);
  font-size: 1.05rem;
  cursor: pointer;
  transition: background 0.15s ease;
}
.num-btn:hover { background: var(--btn-bg-hover); }
.num-btn:disabled { opacity: 0.3; cursor: default; }

.action-row {
  display: flex;
  gap: 8px;
  width: 100%;
  flex-wrap: wrap;
  justify-content: center;
}
.action-btn {
  font-family: inherit;
  flex: 1 1 auto;
  min-width: 90px;
  padding: 9px 10px;
  border-radius: 8px;
  border: 1px solid var(--border);
  background: var(--btn-bg);
  color: var(--text);
  font-size: 0.82rem;
  cursor: pointer;
  display: flex;
  align-items: center;
  justify-content: center;
  gap: 6px;
  transition: background 0.15s ease, border-color 0.15s ease;
}
.action-btn:hover { background: var(--btn-bg-hover); }
.action-btn.toggle-on {
  border-color: var(--accent-2);
  color: var(--accent-2);
}
.action-btn.primary {
  background: var(--accent);
  border-color: var(--accent);
  color: var(--on-accent);
}

.win-banner {
  display: none;
  width: 100%;
  max-width: 460px;
  background: var(--panel);
  border: 1px solid var(--accent-2);
  color: var(--accent-2);
  border-radius: 10px;
  padding: 14px 16px;
  text-align: center;
  font-size: 0.95rem;
}
.win-banner.show { display: block; }

footer {
  color: var(--text-dim);
  font-size: 0.72rem;
  text-align: center;
  margin-top: 6px;
}