:root {
  --bg: #0f1115;
  --panel: #171a21;
  --panel-2: #1e222b;
  --fg: #e6e8ec;
  --muted: #8a93a6;
  --accent: #f5c26b;
  --accent-2: #7cc4ff;
  --border: #272b35;
  --green: #9ae6b4;
  --red: #fca5a5;
  --grid-border: #4a5060;
  --cell-bg: #1e222b;
  --cell-given: #e6e8ec;
  --cell-user: #7cc4ff;
  --cell-selected: rgba(245, 194, 107, 0.18);
  --cell-conflict: rgba(252, 165, 165, 0.22);
  --cell-hint: rgba(154, 230, 180, 0.18);
  --cell-hint-target: rgba(154, 230, 180, 0.35);
}

*,
*::before,
*::after {
  margin: 0;
  padding: 0;
  box-sizing: border-box;
}

body {
  font-family: -apple-system, BlinkMacSystemFont, "Segoe UI", "Hiragino Sans",
    "Hiragino Kaku Gothic ProN", Meiryo, sans-serif;
  font-size: 15px;
  line-height: 1.6;
  background: var(--bg);
  color: var(--fg);
  min-height: 100dvh;
  display: flex;
  flex-direction: column;
}

/* --- Header --- */
header {
  max-width: 520px;
  width: 100%;
  margin: 0 auto;
  padding: 24px 24px 0;
}

.title-row {
  display: flex;
  justify-content: space-between;
  align-items: center;
  gap: 12px;
}

h1 {
  font-size: 28px;
  font-weight: 700;
  color: var(--accent);
}

.timer-box {
  background: var(--panel);
  border: 1px solid var(--border);
  border-radius: 8px;
  padding: 4px 14px;
  display: flex;
  align-items: center;
  gap: 8px;
  font-size: 13px;
  color: var(--muted);
}

.timer-box strong {
  color: var(--fg);
  font-variant-numeric: tabular-nums;
  font-size: 18px;
}

#subtitle {
  color: var(--muted);
  font-size: 13px;
  margin-top: 4px;
}

.top-controls {
  display: flex;
  flex-wrap: wrap;
  align-items: center;
  gap: 8px;
  margin-top: 16px;
}

button.primary {
  background: var(--accent);
  color: #0f1115;
  border: none;
  border-radius: 6px;
  padding: 7px 16px;
  font-size: 14px;
  font-weight: 600;
  cursor: pointer;
  transition: opacity 0.15s;
}

button.primary:hover { opacity: 0.85; }

button.secondary {
  background: var(--panel-2);
  color: var(--accent-2);
  border: 1px solid var(--border);
  border-radius: 6px;
  padding: 7px 16px;
  font-size: 14px;
  font-weight: 600;
  cursor: pointer;
  transition: opacity 0.15s;
}

button.secondary:hover { opacity: 0.85; }

.group {
  display: flex;
  align-items: center;
  gap: 6px;
  font-size: 13px;
  color: var(--muted);
}

select {
  background: var(--panel);
  color: var(--fg);
  border: 1px solid var(--border);
  border-radius: 6px;
  padding: 5px 8px;
  font-size: 13px;
  cursor: pointer;
}

/* --- Main --- */
main {
  max-width: 520px;
  width: 100%;
  margin: 0 auto;
  padding: 20px 24px;
  flex: 1;
}

/* --- Board --- */
.board-wrap {
  position: relative;
  aspect-ratio: 1;
  max-width: 468px;
  margin: 0 auto;
}

.board {
  display: grid;
  grid-template-columns: repeat(9, 1fr);
  grid-template-rows: repeat(9, 1fr);
  width: 100%;
  height: 100%;
  border: 2px solid var(--grid-border);
  border-radius: 8px;
  overflow: hidden;
}

.cell {
  display: flex;
  align-items: center;
  justify-content: center;
  background: var(--cell-bg);
  color: var(--cell-user);
  font-size: clamp(16px, 4.5vw, 24px);
  font-weight: 500;
  border: 1px solid var(--border);
  cursor: pointer;
  transition: background 0.1s;
  outline: none;
  font-family: inherit;
}

.cell:hover {
  background: rgba(255, 255, 255, 0.04);
}

.cell.given {
  color: var(--cell-given);
  font-weight: 700;
}

.cell.selected {
  background: var(--cell-selected);
}

.cell.conflict {
  background: var(--cell-conflict);
  color: var(--red);
}

.cell.same-digit {
  outline: 2px solid var(--accent-2);
  outline-offset: -2px;
  background: rgba(124, 196, 255, 0.12);
}

.cell.hint-highlight {
  background: var(--cell-hint);
}

.cell.hint-target {
  background: var(--cell-hint-target);
  outline: 2px solid var(--green);
  outline-offset: -2px;
}

/* 3×3 box borders */
.cell.border-top { border-top: 2px solid var(--grid-border); }
.cell.border-left { border-left: 2px solid var(--grid-border); }
.cell.border-bottom { border-bottom: 2px solid var(--grid-border); }
.cell.border-right { border-right: 2px solid var(--grid-border); }

/* --- Overlay --- */
.overlay {
  position: absolute;
  inset: 0;
  display: flex;
  flex-direction: column;
  align-items: center;
  justify-content: center;
  gap: 12px;
  background: rgba(15, 17, 21, 0.88);
  border-radius: 8px;
  z-index: 10;
}

.overlay[hidden] {
  display: none;
}

.overlay p {
  font-size: 22px;
  font-weight: 700;
  color: var(--green);
}

.overlay .overlay-time {
  font-size: 16px;
  font-weight: 400;
  color: var(--muted);
}

.overlay .overlay-time strong {
  color: var(--fg);
}

/* --- Hint message --- */
.hint-message {
  margin-top: 12px;
  padding: 10px 16px;
  border-radius: 8px;
  font-size: 14px;
  line-height: 1.5;
}

.hint-message.hint {
  background: rgba(154, 230, 180, 0.12);
  color: var(--green);
  border: 1px solid rgba(154, 230, 180, 0.25);
}

.hint-message.info {
  background: rgba(124, 196, 255, 0.12);
  color: var(--accent-2);
  border: 1px solid rgba(124, 196, 255, 0.25);
}

.hint-message.error {
  background: rgba(252, 165, 165, 0.12);
  color: var(--red);
  border: 1px solid rgba(252, 165, 165, 0.25);
}

/* --- Numpad --- */
.numpad {
  display: grid;
  grid-template-columns: repeat(5, 1fr);
  gap: 6px;
  margin-top: 16px;
  max-width: 320px;
  margin-left: auto;
  margin-right: auto;
}

.numpad-btn {
  background: var(--panel);
  color: var(--fg);
  border: 1px solid var(--border);
  border-radius: 8px;
  font-size: 20px;
  font-weight: 600;
  padding: 12px 0;
  cursor: pointer;
  transition: background 0.1s;
  font-family: inherit;
}

.numpad-btn:hover {
  background: var(--panel-2);
}

.numpad-btn.numpad-clear {
  color: var(--red);
}

.numpad-btn.done,
.numpad-btn:disabled {
  opacity: 0.3;
  cursor: default;
  color: var(--border);
  background: var(--panel);
}

.numpad-btn.done:hover,
.numpad-btn:disabled:hover {
  background: var(--panel);
}

/* --- Footer --- */
footer {
  max-width: 520px;
  width: 100%;
  margin: 0 auto;
  padding: 16px 24px 24px;
  text-align: center;
  font-size: 12px;
  color: var(--muted);
}

/* --- Responsive --- */
@media (max-width: 480px) {
  header, main, footer {
    padding-left: 12px;
    padding-right: 12px;
  }

  h1 { font-size: 24px; }

  .top-controls { gap: 6px; }

  .numpad {
    max-width: 100%;
  }
}