:root {
  --bg-deep: #0a0a12;
  --bg-panel: rgba(255, 255, 255, 0.04);
  --border-subtle: rgba(255, 255, 255, 0.08);
  --text-primary: #f0f0f5;
  --text-muted: #8888a0;
  --accent-cyan: #00e5ff;
  --accent-purple: #a855f7;
  --grid-line: rgba(255, 255, 255, 0.1);
  --grid-band: rgba(0, 229, 255, 0.35);
  --state-error: #f43f5e;
  --font: 'Outfit', system-ui, sans-serif;
}

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

body {
  font-family: var(--font);
  background: var(--bg-deep);
  color: var(--text-primary);
  min-height: 100vh;
  overflow: hidden;
}

.game-layout {
  display: flex;
  flex-direction: column;
  height: 100vh;
}

/* ---- Header ---- */
.game-header {
  display: flex;
  align-items: center;
  gap: 1.25rem;
  padding: 1rem 1.5rem;
  border-bottom: 1px solid var(--border-subtle);
  flex-wrap: wrap;
}

.back-link {
  color: var(--text-muted);
  text-decoration: none;
  font-size: 0.9rem;
  transition: color 0.2s;
}

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

.game-header h1 {
  font-size: 1.5rem;
  font-weight: 600;
  background: linear-gradient(135deg, var(--text-primary), var(--accent-cyan));
  -webkit-background-clip: text;
  -webkit-text-fill-color: transparent;
  background-clip: text;
}

/* ---- Difficulty segmented control ---- */
.seg {
  display: flex;
  gap: 2px;
  padding: 3px;
  border: 1px solid var(--border-subtle);
  border-radius: 100px;
  background: var(--bg-panel);
}

.seg__btn {
  font-family: var(--font);
  font-size: 0.8rem;
  font-weight: 600;
  padding: 0.4rem 0.9rem;
  border: none;
  border-radius: 100px;
  background: transparent;
  color: var(--text-muted);
  cursor: pointer;
  transition: background 0.2s, color 0.2s;
}

.seg__btn:hover {
  color: var(--text-primary);
}

.seg__btn.is-active {
  background: linear-gradient(135deg, rgba(0, 229, 255, 0.9), rgba(0, 153, 204, 0.9));
  color: #0a0a12;
  box-shadow: 0 0 16px rgba(0, 229, 255, 0.3);
}

.tool-btn {
  font-family: var(--font);
  font-size: 0.85rem;
  font-weight: 600;
  padding: 0.5rem 1.1rem;
  border: 1px solid var(--border-subtle);
  border-radius: 100px;
  background: var(--bg-panel);
  color: var(--text-primary);
  cursor: pointer;
  transition: border-color 0.2s, color 0.2s, opacity 0.2s;
}

.tool-btn:hover:not(:disabled) {
  border-color: rgba(0, 229, 255, 0.4);
  color: var(--accent-cyan);
}

.tool-btn:disabled {
  opacity: 0.4;
  cursor: default;
}

.tool-btn.is-active {
  border-color: rgba(168, 85, 247, 0.6);
  color: var(--accent-purple);
  box-shadow: 0 0 16px rgba(168, 85, 247, 0.2);
}

.tool-btn--primary {
  margin-left: auto;
}

/* ---- Container ---- */
.game-container {
  flex: 1;
  display: flex;
  flex-direction: column;
  align-items: center;
  gap: 0.9rem;
  padding: 0.9rem 1rem;
  min-height: 0;
}

.stat-bar {
  display: flex;
  gap: 2rem;
}

.stat {
  display: flex;
  flex-direction: column;
  align-items: center;
  gap: 0.15rem;
}

.stat__label {
  font-size: 0.65rem;
  text-transform: uppercase;
  letter-spacing: 0.1em;
  color: var(--text-muted);
}

.stat__value {
  font-size: 1.4rem;
  font-weight: 700;
  color: var(--accent-cyan);
}

.stat__value--text {
  font-size: 0.95rem;
  font-weight: 600;
  color: var(--accent-purple);
}

/* ---- Board ---- */
.board-wrap {
  flex: 1;
  min-height: 0;
  display: flex;
  align-items: center;
  justify-content: center;
  width: 100%;
}

.board {
  position: relative;
  height: 100%;
  max-height: min(62vh, 560px);
  aspect-ratio: 1;
  max-width: 100%;
  display: grid;
  grid-template-columns: repeat(9, 1fr);
  background:
    radial-gradient(circle at 25% 15%, rgba(0, 229, 255, 0.06), transparent 60%),
    radial-gradient(circle at 80% 90%, rgba(168, 85, 247, 0.06), transparent 60%),
    var(--bg-panel);
  border: 2px solid var(--grid-band);
  border-radius: 12px;
  overflow: hidden;
  transition: box-shadow 0.4s ease;
}

.board--loading {
  visibility: hidden;
}

.board--solved {
  box-shadow: 0 0 50px rgba(0, 229, 255, 0.35);
}

.cell {
  position: relative;
  display: flex;
  align-items: center;
  justify-content: center;
  padding: 0;
  font-family: var(--font);
  background: transparent;
  border: none;
  border-right: 1px solid var(--grid-line);
  border-bottom: 1px solid var(--grid-line);
  color: var(--accent-cyan);
  cursor: pointer;
  transition: background 0.12s ease;
}

.cell--band-r { border-right: 2px solid var(--grid-band); }
.cell--band-b { border-bottom: 2px solid var(--grid-band); }
.cell--last-col { border-right: none; }
.cell--last-row { border-bottom: none; }

.cell:focus { outline: none; }

.cell__value {
  font-size: clamp(1rem, 4.4vmin, 2rem);
  font-weight: 600;
  line-height: 1;
  pointer-events: none;
}

/* Highlight bands: peers first so the stronger states can override them. */
.cell--peer { background: rgba(255, 255, 255, 0.045); }
.cell--match { background: rgba(168, 85, 247, 0.2); }
.cell--selected { background: rgba(0, 229, 255, 0.22); }

.cell--given {
  color: var(--text-primary);
  font-weight: 700;
  cursor: default;
}

.cell--hinted { color: #22c55e; }

.cell--error {
  color: var(--state-error);
  background: rgba(244, 63, 94, 0.16);
}

.cell--error.cell--selected { background: rgba(244, 63, 94, 0.3); }

.cell--flash { animation: cell-shake 0.35s ease; }

@keyframes cell-shake {
  0%, 100% { transform: translateX(0); }
  25% { transform: translateX(-3px); }
  75% { transform: translateX(3px); }
}

/* ---- Pencil marks ---- */
.cell__notes {
  position: absolute;
  inset: 8%;
  display: none;
  grid-template-columns: repeat(3, 1fr);
  grid-template-rows: repeat(3, 1fr);
  pointer-events: none;
}

.cell--has-notes .cell__notes { display: grid; }

.cell__notes span {
  display: flex;
  align-items: center;
  justify-content: center;
  font-size: clamp(0.4rem, 1.5vmin, 0.7rem);
  line-height: 1;
  color: var(--text-muted);
  visibility: hidden;
}

.cell__notes span.is-on { visibility: visible; }

/* ---- Number pad ---- */
.pad {
  display: flex;
  flex-direction: column;
  align-items: center;
  gap: 0.6rem;
  width: 100%;
}

.pad__tools {
  display: flex;
  gap: 0.5rem;
  flex-wrap: wrap;
  justify-content: center;
}

.numpad {
  display: grid;
  grid-template-columns: repeat(9, 1fr);
  gap: 0.4rem;
  width: 100%;
  max-width: 520px;
}

.pad-btn {
  position: relative;
  font-family: var(--font);
  aspect-ratio: 4 / 5;
  display: flex;
  align-items: center;
  justify-content: center;
  border: 1px solid var(--border-subtle);
  border-radius: 8px;
  background: var(--bg-panel);
  color: var(--accent-cyan);
  cursor: pointer;
  transition: border-color 0.15s, background 0.15s, transform 0.05s, opacity 0.2s;
}

.pad-btn:hover {
  border-color: rgba(0, 229, 255, 0.45);
  background: rgba(0, 229, 255, 0.08);
}

.pad-btn:active { transform: translateY(1px); }

.pad-btn.is-done {
  opacity: 0.3;
  color: var(--text-muted);
}

.pad-btn__digit {
  font-size: clamp(1.1rem, 3.4vmin, 1.6rem);
  font-weight: 600;
  line-height: 1;
}

.pad-btn__count {
  position: absolute;
  right: 4px;
  bottom: 2px;
  font-size: 0.6rem;
  font-weight: 600;
  color: var(--text-muted);
}

/* ---- Toast ---- */
.toast {
  position: fixed;
  top: 5rem;
  left: 50%;
  transform: translateX(-50%);
  background: var(--text-primary);
  color: var(--bg-deep);
  font-weight: 600;
  font-size: 0.9rem;
  padding: 0.7rem 1.2rem;
  border-radius: 8px;
  opacity: 0;
  pointer-events: none;
  transition: opacity 0.2s ease;
  z-index: 20;
}

.toast--show { opacity: 1; }

/* ---- End overlay ---- */
.overlay {
  position: fixed;
  inset: 0;
  display: flex;
  align-items: center;
  justify-content: center;
  background: rgba(10, 10, 18, 0.75);
  backdrop-filter: blur(8px);
  z-index: 10;
}

.overlay--hidden { display: none; }

.overlay-content {
  text-align: center;
  padding: 2.5rem;
  background: var(--bg-panel);
  border: 1px solid var(--border-subtle);
  border-radius: 16px;
  backdrop-filter: blur(12px);
  max-width: 90vw;
  width: 30rem;
}

.overlay-content h2 {
  font-size: 2rem;
  font-weight: 700;
  margin-bottom: 0.5rem;
  background: linear-gradient(135deg, var(--text-primary), var(--accent-cyan));
  -webkit-background-clip: text;
  -webkit-text-fill-color: transparent;
  background-clip: text;
}

.overlay-content p {
  color: var(--text-muted);
  line-height: 1.5;
  margin-bottom: 1.5rem;
}

.end-stats {
  display: flex;
  justify-content: center;
  gap: 1.5rem;
  margin-bottom: 1.5rem;
}

.end-stat { text-align: center; }

.end-stat__value {
  font-size: 1.6rem;
  font-weight: 700;
  color: var(--accent-cyan);
}

.end-stat__label {
  display: block;
  font-size: 0.7rem;
  text-transform: uppercase;
  letter-spacing: 0.08em;
  color: var(--text-muted);
  margin-top: 0.2rem;
}

.btn-start {
  font-family: var(--font);
  font-size: 1rem;
  font-weight: 600;
  padding: 0.75rem 2rem;
  border: none;
  border-radius: 100px;
  background: linear-gradient(135deg, #00e5ff, #0099cc);
  color: #0a0a12;
  cursor: pointer;
  transition: transform 0.2s, box-shadow 0.2s;
}

.btn-start:hover {
  transform: scale(1.05);
  box-shadow: 0 0 30px rgba(0, 229, 255, 0.4);
}

@media (max-width: 620px) {
  .game-header { gap: 0.75rem; padding: 0.85rem 1rem; }
  .game-header h1 { font-size: 1.25rem; }
  .seg__btn { padding: 0.35rem 0.6rem; font-size: 0.72rem; }
  .stat-bar { gap: 1.2rem; }
  .stat__value { font-size: 1.15rem; }
  .stat__value--text { font-size: 0.8rem; }
  .board { max-height: min(46vh, 440px); }
  .tool-btn { padding: 0.45rem 0.85rem; font-size: 0.78rem; }
}