/* ── Design tokens ─────────────────────────────────────────────────────────── */
:root {
  color-scheme: dark;
  font-family: "Trebuchet MS", "Gill Sans", sans-serif;

  /* Base palette (matches Snake game) */
  --bg: #0c1311;
  --bg-accent: #12201b;
  --panel: rgba(18, 30, 26, 0.92);
  --panel-border: rgba(142, 179, 144, 0.22);
  --text: #edf4ee;
  --muted: #9eb4a1;
  --accent: #74d680;
  --accent-strong: #2d8f47;
  --danger: #ff7878;

  /* Sudoku-specific */
  --cell-size: 56px;
  --cell-given:   #edf4ee;
  --cell-user:    #74d680;
  --cell-error:   #ff7878;
  --cell-pencil:  #9eb4a1;
  --cell-selected: rgba(116, 214, 128, 0.20);
  --cell-peer:     rgba(116, 214, 128, 0.07);
  --cell-same-num: rgba(116, 214, 128, 0.15);
  --box-border:    rgba(142, 179, 144, 0.55);
  --cell-border:   rgba(142, 179, 144, 0.15);
}

/* ── Back Link ─────────────────────────────────────────────────────────────── */
.back-link {
  display: inline-block;
  color: var(--muted);
  text-decoration: none;
  font-size: 0.82rem;
  letter-spacing: 0.04em;
  margin-bottom: 6px;
  transition: color 120ms ease;
}

.back-link:hover {
  color: var(--accent);
}

/* ── Reset ─────────────────────────────────────────────────────────────────── */
* { box-sizing: border-box; }

html, body {
  width: 100%;
  height: 100%;
}

body {
  margin: 0;
  background:
    radial-gradient(circle at top left, rgba(116, 214, 128, 0.14), transparent 28%),
    radial-gradient(circle at bottom right, rgba(73, 134, 96, 0.18), transparent 34%),
    linear-gradient(180deg, var(--bg-accent), var(--bg));
  color: var(--text);
}

button, input { font: inherit; }

/* ── Layout ────────────────────────────────────────────────────────────────── */
.app {
  width: 100vw;
  min-height: 100vh;
  padding: 24px;
  display: grid;
  grid-template-columns: minmax(0, 1fr) minmax(280px, 340px);
  gap: 20px;
}

.panel {
  background: var(--panel);
  border: 1px solid var(--panel-border);
  border-radius: 18px;
  box-shadow: 0 20px 40px rgba(0, 0, 0, 0.24);
  backdrop-filter: blur(10px);
}

.hidden { display: none !important; }

/* ── Play area ─────────────────────────────────────────────────────────────── */
.play-area {
  min-height: calc(100vh - 48px);
  padding: 20px;
  display: grid;
  grid-template-rows: auto auto auto minmax(0, 1fr);
  gap: 18px;
  align-items: start;
}

.play-header {
  display: flex;
  justify-content: space-between;
  align-items: start;
  gap: 12px;
}

.eyebrow {
  margin: 0 0 4px;
  text-transform: uppercase;
  letter-spacing: 0.16em;
  font-size: 0.72rem;
  color: var(--muted);
}

h1, h2 { margin: 0; }

h1 { font-size: clamp(2rem, 3vw, 2.8rem); line-height: 1; }

/* ── Stat cards ────────────────────────────────────────────────────────────── */
.stats {
  display: grid;
  grid-template-columns: repeat(4, minmax(0, 1fr));
  gap: 12px;
}

.stat-card {
  padding: 12px 14px;
  border-radius: 14px;
  background: rgba(255, 255, 255, 0.03);
  border: 1px solid rgba(255, 255, 255, 0.04);
  display: grid;
  gap: 6px;
}

.status-card { border-color: rgba(116, 214, 128, 0.18); }

.stat-label {
  font-size: 0.8rem;
  text-transform: uppercase;
  letter-spacing: 0.1em;
  color: var(--muted);
}

.stat-value {
  font-size: clamp(1rem, 2vw, 1.4rem);
  font-weight: 700;
}

/* ── Sudoku Board ──────────────────────────────────────────────────────────── */
.board {
  display: grid;
  grid-template-columns: repeat(9, var(--cell-size));
  grid-template-rows: repeat(9, var(--cell-size));
  border: 2px solid var(--box-border);
  border-radius: 10px;
  overflow: hidden;
  width: fit-content;
  justify-self: center;
  align-self: center;
  outline: none;
}

/* ── Cell ──────────────────────────────────────────────────────────────────── */
.cell {
  width: var(--cell-size);
  height: var(--cell-size);
  display: flex;
  align-items: center;
  justify-content: center;
  cursor: pointer;
  position: relative;
  border-right: 1px solid var(--cell-border);
  border-bottom: 1px solid var(--cell-border);
  font-size: calc(var(--cell-size) * 0.46);
  font-weight: 700;
  transition: background 100ms ease;
  user-select: none;
  -webkit-tap-highlight-color: transparent;
  background: transparent;
}

/* Thick border after every 3rd column (but not the last) */
.cell:nth-child(3n+3):not(:nth-child(9n)) {
  border-right: 2px solid var(--box-border);
}

/* Remove right border on last column (outer border from .board handles it) */
.cell:nth-child(9n) {
  border-right: none;
}

/* Thick border below rows 3 and 6 (cells 19–27 and 46–54) */
.cell:nth-child(n+19):nth-child(-n+27),
.cell:nth-child(n+46):nth-child(-n+54) {
  border-bottom: 2px solid var(--box-border);
}

/* Remove bottom border on last row */
.cell:nth-child(n+73) {
  border-bottom: none;
}

/* ── Cell state classes ────────────────────────────────────────────────────── */
.cell.peer     { background: var(--cell-peer); }
.cell.same-num { background: var(--cell-same-num); }
.cell.selected { background: var(--cell-selected); }

.cell.given    { color: var(--cell-given); }
.cell.user-entry { color: var(--cell-user); }
.cell.error    { color: var(--cell-error) !important; }

/* ── Pencil marks ──────────────────────────────────────────────────────────── */
.pencil-grid {
  display: grid;
  grid-template-columns: repeat(3, 1fr);
  grid-template-rows: repeat(3, 1fr);
  width: 100%;
  height: 100%;
  padding: 2px;
}

.pencil-digit {
  font-size: calc(var(--cell-size) * 0.22);
  font-weight: 400;
  color: var(--cell-pencil);
  display: flex;
  align-items: center;
  justify-content: center;
  line-height: 1;
}

/* ── Mobile numpad ─────────────────────────────────────────────────────────── */
.numpad {
  display: none;
  grid-template-columns: repeat(5, 1fr);
  gap: 8px;
  padding: 4px 0;
}

@media (hover: none) and (pointer: coarse) {
  .numpad { display: grid; }

  .play-area {
    grid-template-rows: auto auto auto auto;
  }
}

.num-btn {
  min-height: 52px;
  border-radius: 14px;
  border: 1px solid rgba(255, 255, 255, 0.1);
  background: rgba(255, 255, 255, 0.06);
  color: var(--text);
  font-size: 1.3rem;
  font-weight: 700;
  cursor: pointer;
  touch-action: manipulation;
  -webkit-tap-highlight-color: transparent;
  transition: background 100ms ease, border-color 100ms ease;
}

.num-btn:hover:not(:disabled) {
  background: rgba(255, 255, 255, 0.11);
  transform: none;
  filter: none;
}

.num-btn:active {
  background: rgba(116, 214, 128, 0.18);
  border-color: rgba(116, 214, 128, 0.35);
}

.num-erase { font-size: 1.1rem; }

/* Pencil mode tint on numpad */
.numpad.pencil-active .num-btn {
  background: rgba(116, 214, 128, 0.10);
  border-color: rgba(116, 214, 128, 0.22);
}

/* ── Sidebar ───────────────────────────────────────────────────────────────── */
.sidebar {
  display: grid;
  gap: 20px;
  align-content: start;
}

.controls-panel,
.leaderboard {
  padding: 18px;
}

/* ── Difficulty toggle ─────────────────────────────────────────────────────── */
.mode-toggle {
  display: flex;
  background: rgba(255, 255, 255, 0.04);
  border: 1px solid rgba(255, 255, 255, 0.07);
  border-radius: 999px;
  padding: 4px;
  gap: 3px;
  margin-bottom: 14px;
}

.mode-toggle-btn {
  flex: 1;
  min-height: 34px;
  padding: 6px 10px;
  border-radius: 999px;
  border: none;
  background: transparent;
  color: var(--muted);
  font-size: 0.85rem;
  font-weight: 600;
  transition: background 160ms ease, color 160ms ease;
  cursor: pointer;
}

.mode-toggle-btn:hover:not(.active) {
  background: rgba(255, 255, 255, 0.06);
  color: var(--text);
  transform: none;
  filter: none;
}

.mode-toggle-btn.active {
  background: linear-gradient(180deg, var(--accent), var(--accent-strong));
  color: #08100d;
}

/* ── Action buttons ────────────────────────────────────────────────────────── */
.controls {
  display: flex;
  flex-wrap: wrap;
  gap: 10px;
}

button {
  min-height: 42px;
  padding: 10px 16px;
  border-radius: 999px;
  border: 1px solid transparent;
  background: linear-gradient(180deg, var(--accent), var(--accent-strong));
  color: #08100d;
  font-weight: 700;
  cursor: pointer;
  transition: transform 120ms ease, opacity 120ms ease, filter 120ms ease;
}

button:hover:not(:disabled) {
  transform: translateY(-1px);
  filter: brightness(1.03);
}

button:disabled {
  opacity: 0.45;
  cursor: not-allowed;
}

.secondary-btn {
  background: rgba(255, 255, 255, 0.04);
  border-color: rgba(255, 255, 255, 0.08);
  color: var(--text);
}

/* ── Toggle (checkbox pill) ────────────────────────────────────────────────── */
.toggle-label {
  display: flex;
  align-items: center;
  gap: 10px;
  font-size: 0.88rem;
  color: var(--muted);
  cursor: pointer;
  user-select: none;
}

.toggle-label input[type="checkbox"] {
  width: 36px;
  height: 20px;
  appearance: none;
  -webkit-appearance: none;
  background: rgba(255, 255, 255, 0.08);
  border: 1px solid rgba(255, 255, 255, 0.12);
  border-radius: 999px;
  position: relative;
  cursor: pointer;
  transition: background 160ms ease;
  flex-shrink: 0;
}

.toggle-label input[type="checkbox"]::after {
  content: "";
  position: absolute;
  width: 14px;
  height: 14px;
  background: var(--muted);
  border-radius: 50%;
  top: 2px;
  left: 2px;
  transition: transform 160ms ease, background 160ms ease;
}

.toggle-label input[type="checkbox"]:checked {
  background: var(--accent-strong);
  border-color: var(--accent);
}

.toggle-label input[type="checkbox"]:checked::after {
  transform: translateX(16px);
  background: var(--accent);
}

/* ── Help text ─────────────────────────────────────────────────────────────── */
.help {
  margin: 14px 0 0;
  color: var(--muted);
  line-height: 1.6;
  font-size: 0.88rem;
}

.help kbd {
  font-family: inherit;
  font-size: 0.82em;
  background: rgba(255,255,255,0.08);
  border: 1px solid rgba(255,255,255,0.12);
  border-radius: 5px;
  padding: 1px 5px;
}

/* ── Leaderboard ───────────────────────────────────────────────────────────── */
.leaderboard-header {
  display: flex;
  justify-content: space-between;
  align-items: baseline;
  gap: 12px;
  margin-bottom: 12px;
}

.lb-tabs { margin-bottom: 12px; }

.leaderboard table {
  width: 100%;
  border-collapse: collapse;
  font-size: 0.9rem;
}

.leaderboard th,
.leaderboard td {
  padding: 8px 6px;
  border-bottom: 1px solid rgba(255, 255, 255, 0.07);
  text-align: left;
}

.leaderboard th {
  font-size: 0.75rem;
  text-transform: uppercase;
  letter-spacing: 0.08em;
  color: var(--muted);
}

.col-r { text-align: right !important; }

.leaderboard tbody tr:last-child td { border-bottom: none; }

.lb-rank {
  font-size: 0.78rem;
  color: var(--muted);
  min-width: 18px;
}

.lb-rank.gold   { color: #f5c842; font-weight: 700; }
.lb-rank.silver { color: #b0b8c1; font-weight: 700; }
.lb-rank.bronze { color: #cd7f32; font-weight: 700; }

.lb-name { max-width: 90px; overflow: hidden; text-overflow: ellipsis; white-space: nowrap; }

.lb-highlight td { color: var(--accent); }

.lb-empty {
  text-align: center;
  color: var(--muted);
  padding: 20px 0 !important;
  font-size: 0.88rem;
}

/* ── Modal input ───────────────────────────────────────────────────────────── */
.modal-field {
  display: grid;
  gap: 8px;
  text-align: left;
  margin-bottom: 4px;
}

.modal-label {
  font-size: 0.85rem;
  color: var(--muted);
}

.modal input[type="text"] {
  width: 100%;
  min-height: 46px;
  padding: 0 14px;
  border-radius: 12px;
  border: 1px solid rgba(255, 255, 255, 0.08);
  background: rgba(255, 255, 255, 0.04);
  color: var(--text);
}

.modal input[type="text"]::placeholder {
  color: rgba(237, 244, 238, 0.35);
}

.modal input[type="text"]:focus {
  outline: none;
  border-color: rgba(116, 214, 128, 0.45);
}

.modal-actions { gap: 10px; }

/* ── Win modal ─────────────────────────────────────────────────────────────── */
.modal-overlay {
  position: fixed;
  inset: 0;
  display: flex;
  align-items: center;
  justify-content: center;
  padding: 24px;
  background: rgba(5, 8, 7, 0.74);
  z-index: 10;
}

.modal {
  width: min(92vw, 380px);
  padding: 28px 24px;
  border-radius: 20px;
  background: linear-gradient(180deg, #15231d, #0f1814);
  border: 1px solid rgba(255, 255, 255, 0.08);
  box-shadow: 0 28px 60px rgba(0, 0, 0, 0.35);
  text-align: center;
}

.modal p {
  margin: 10px 0 18px;
  color: var(--muted);
}

.modal-actions {
  margin-top: 14px;
  display: flex;
  justify-content: center;
}

/* ── Responsive ────────────────────────────────────────────────────────────── */
@media (max-width: 980px) {
  :root { --cell-size: 52px; }

  .app {
    grid-template-columns: 1fr;
  }

  .play-area {
    min-height: auto;
  }

  .sidebar {
    grid-template-columns: repeat(2, minmax(0, 1fr));
  }
}

@media (max-width: 720px) {
  :root { --cell-size: 40px; }

  .app {
    padding: 14px;
    gap: 14px;
  }

  .play-area {
    min-height: auto;
    padding: 16px;
  }

  .play-header {
    flex-direction: column;
    align-items: stretch;
  }

  .stats {
    grid-template-columns: repeat(2, minmax(0, 1fr));
  }

  .sidebar {
    grid-template-columns: 1fr;
    gap: 14px;
  }

  .controls {
    flex-direction: column;
  }

  button, .secondary-btn {
    width: 100%;
  }
}

@media (max-width: 420px) {
  :root { --cell-size: calc((100vw - 32px - 4px) / 9); }
}

@media (prefers-reduced-motion: reduce) {
  * {
    transition-duration: 0.01ms !important;
    animation-duration: 0.01ms !important;
  }
}