:root {
  color-scheme: light;
  --page: #f3f6fb;
  --card: #ffffff;
  --ink: #172235;
  --muted: #718096;
  --line: #dfe6f0;
  --line-strong: #aebbd0;
  --accent: #2e6ee8;
  --accent-dark: #1f55b7;
  --accent-soft: #e4edff;
  --related: #f2f6fd;
  --danger: #bd3b42;
  --danger-soft: #fff0ef;
  --success: #237653;
  --safe-top: env(safe-area-inset-top, 0px);
  --safe-right: env(safe-area-inset-right, 0px);
  --safe-bottom: env(safe-area-inset-bottom, 0px);
  --safe-left: env(safe-area-inset-left, 0px);
  font-family: -apple-system, BlinkMacSystemFont, "Segoe UI", sans-serif;
  font-synthesis: none;
}

* {
  box-sizing: border-box;
}

html {
  min-height: 100%;
  background: var(--page);
}

body {
  min-width: 0;
  min-height: 100svh;
  margin: 0;
  overflow-x: hidden;
  background:
    radial-gradient(circle at 15% 0%, rgba(218, 231, 255, 0.7), transparent 28rem),
    var(--page);
  color: var(--ink);
  -webkit-font-smoothing: antialiased;
}

button,
select {
  font: inherit;
}

button {
  -webkit-tap-highlight-color: transparent;
  touch-action: manipulation;
}

button:focus-visible,
select:focus-visible,
input:focus-visible + .toggle-track {
  outline: 3px solid rgba(46, 110, 232, 0.34);
  outline-offset: 2px;
}

button:disabled {
  cursor: default;
}

.app-shell {
  width: min(100%, 580px);
  min-height: 100svh;
  margin: 0 auto;
  padding: calc(18px + var(--safe-top)) max(14px, var(--safe-right)) calc(28px + var(--safe-bottom)) max(14px, var(--safe-left));
}

.app-header,
.brand-lockup,
.game-tools,
.puzzle-heading,
.controls-heading,
.toggle-field,
.undo-button,
.new-game-button,
.secondary-button {
  display: flex;
  align-items: center;
}

.app-header {
  justify-content: space-between;
  gap: 14px;
  margin-bottom: 16px;
}

.brand-lockup {
  min-width: 0;
  gap: 10px;
}

.brand-mark {
  display: grid;
  flex: 0 0 42px;
  width: 42px;
  height: 42px;
  place-items: center;
  border: 1px solid #c5d6f5;
  border-radius: 13px;
  background: var(--accent-soft);
  color: var(--accent-dark);
  font-size: 1.35rem;
  font-weight: 800;
}

.eyebrow {
  margin: 0 0 3px;
  color: var(--muted);
  font-size: 0.68rem;
  font-weight: 700;
  letter-spacing: 0.12em;
  line-height: 1.2;
  text-transform: uppercase;
}

h1 {
  margin: 0;
  font-size: clamp(1.45rem, 6vw, 1.8rem);
  letter-spacing: -0.04em;
  line-height: 1;
}

.new-game-button,
.secondary-button,
.undo-button,
.number-key {
  border: 1px solid var(--line);
  color: var(--ink);
  cursor: pointer;
}

.new-game-button {
  min-height: 46px;
  padding: 0 15px;
  border-color: var(--accent);
  border-radius: 14px;
  background: var(--accent);
  box-shadow: 0 5px 12px rgba(46, 110, 232, 0.18);
  color: #fff;
  font-size: 0.88rem;
  font-weight: 750;
  white-space: nowrap;
}

.new-game-button:active {
  background: var(--accent-dark);
  transform: translateY(1px);
}

.game-card,
.controls-card {
  border: 1px solid rgba(215, 224, 237, 0.95);
  border-radius: 24px;
  background: rgba(255, 255, 255, 0.92);
  box-shadow: 0 12px 36px rgba(38, 61, 96, 0.08);
}

.game-card {
  padding: 14px 12px 16px;
}

.game-tools {
  gap: 8px;
  margin-bottom: 15px;
}

.difficulty-field {
  display: grid;
  flex: 1 1 auto;
  gap: 4px;
  min-width: 0;
  color: var(--muted);
  font-size: 0.68rem;
  font-weight: 700;
  letter-spacing: 0.04em;
  text-transform: uppercase;
}

.difficulty-field select {
  width: 100%;
  min-height: 44px;
  padding: 0 30px 0 11px;
  border: 1px solid var(--line);
  border-radius: 12px;
  outline: none;
  background-color: #fbfcfe;
  color: var(--ink);
  font-size: 0.9rem;
  font-weight: 700;
  letter-spacing: normal;
  text-transform: none;
}

.toggle-field {
  flex: 0 0 auto;
  gap: 6px;
  align-self: flex-end;
  min-height: 44px;
  color: var(--muted);
  font-size: 0.72rem;
  font-weight: 700;
  white-space: nowrap;
}

.toggle-field input {
  position: absolute;
  width: 1px;
  height: 1px;
  overflow: hidden;
  clip: rect(0 0 0 0);
  clip-path: inset(50%);
  white-space: nowrap;
}

.toggle-track {
  position: relative;
  display: inline-block;
  flex: 0 0 36px;
  width: 36px;
  height: 22px;
  border-radius: 99px;
  background: #c8d2e1;
  transition: background 160ms ease;
}

.toggle-track span {
  position: absolute;
  top: 3px;
  left: 3px;
  width: 16px;
  height: 16px;
  border-radius: 50%;
  background: #fff;
  box-shadow: 0 1px 3px rgba(23, 34, 53, 0.22);
  transition: transform 160ms ease;
}

.toggle-field input:checked + .toggle-track {
  background: var(--accent);
}

.toggle-field input:checked + .toggle-track span {
  transform: translateX(14px);
}

.undo-button {
  flex: 0 0 auto;
  justify-content: center;
  gap: 5px;
  align-self: flex-end;
  min-height: 44px;
  padding: 0 9px;
  border-radius: 12px;
  background: #fbfcfe;
  font-size: 0.76rem;
  font-weight: 700;
}

.undo-button span:first-child {
  font-size: 1.35rem;
  font-weight: 400;
  line-height: 1;
}

.undo-button:disabled,
.secondary-button:disabled,
.number-key:disabled {
  border-color: #edf0f5;
  background: #f7f9fc;
  color: #aeb8c8;
  opacity: 0.72;
}

.puzzle-heading,
.controls-heading {
  justify-content: space-between;
  gap: 10px;
}

.puzzle-heading {
  margin: 0 3px 10px;
}

.puzzle-status,
.controls-help {
  margin: 0;
  color: var(--ink);
  font-size: 0.86rem;
  font-weight: 700;
}

.status-dot {
  width: 10px;
  height: 10px;
  flex: 0 0 10px;
  border-radius: 50%;
  background: #6bc29a;
  box-shadow: 0 0 0 4px #e4f5ec;
}

.status-dot.is-busy {
  background: #e3a83d;
  box-shadow: 0 0 0 4px #fff2d7;
}

.status-dot.is-complete {
  background: var(--success);
  box-shadow: 0 0 0 4px #def4e9;
}

.board-wrap {
  position: relative;
}

.sudoku-board {
  display: grid;
  grid-template-columns: repeat(9, minmax(0, 1fr));
  grid-template-rows: repeat(9, minmax(44px, 1fr));
  width: 100%;
  min-height: 396px;
  aspect-ratio: 1;
  overflow: hidden;
  border: 2px solid var(--line-strong);
  border-radius: 15px;
  background: var(--line-strong);
  box-shadow: 0 4px 12px rgba(37, 59, 91, 0.06);
}

.cell {
  position: relative;
  display: grid;
  min-width: 0;
  min-height: 44px;
  place-items: center;
  padding: 0;
  border: 0;
  border-right: 1px solid var(--line);
  border-bottom: 1px solid var(--line);
  border-radius: 0;
  outline: none;
  background: #fff;
  color: var(--ink);
  cursor: pointer;
  transition: background-color 120ms ease, color 120ms ease;
}

.cell:nth-child(9n) {
  border-right: 0;
}

.cell:nth-child(n + 73) {
  border-bottom: 0;
}

.cell.box-right {
  border-right: 2px solid var(--line-strong);
}

.cell.box-bottom {
  border-bottom: 2px solid var(--line-strong);
}

.cell.is-related {
  background: var(--related);
}

.cell.is-same-number {
  background: #eaf1ff;
  color: var(--accent-dark);
}

.cell.is-selected {
  z-index: 1;
  background: var(--accent-soft);
  box-shadow: inset 0 0 0 2px var(--accent);
  color: var(--accent-dark);
}

.cell.is-conflict {
  background: var(--danger-soft);
  color: var(--danger);
}

.cell.is-selected.is-conflict {
  background: #ffe1df;
  box-shadow: inset 0 0 0 2px var(--danger);
}

.cell.is-given {
  font-weight: 800;
}

.cell-value {
  position: relative;
  z-index: 1;
  font-size: clamp(1.25rem, 6.5vw, 1.72rem);
  line-height: 1;
}

.cell-notes {
  display: grid;
  grid-template-columns: repeat(3, 1fr);
  grid-template-rows: repeat(3, 1fr);
  position: absolute;
  inset: 8% 7%;
  color: #6f82a2;
  font-size: clamp(0.48rem, 2.4vw, 0.7rem);
  font-weight: 700;
  line-height: 1;
  pointer-events: none;
}

.cell-notes span {
  display: grid;
  place-items: center;
  min-width: 0;
  min-height: 0;
}

.cell-notes:empty {
  display: none;
}

.cell.has-value .cell-notes {
  display: none;
}

.cell:active {
  background: #dce8ff;
}

.generating-cover {
  position: absolute;
  inset: 0;
  display: flex;
  align-items: center;
  justify-content: center;
  gap: 9px;
  border-radius: 14px;
  background: rgba(255, 255, 255, 0.86);
  color: var(--accent-dark);
  font-size: 0.9rem;
  font-weight: 750;
  backdrop-filter: blur(3px);
}

.generating-cover[hidden] {
  display: none;
}

.spinner {
  width: 17px;
  height: 17px;
  border: 2px solid #c9dafa;
  border-top-color: var(--accent);
  border-radius: 50%;
  animation: spin 700ms linear infinite;
}

@keyframes spin {
  to { transform: rotate(360deg); }
}

.message {
  min-height: 21px;
  margin: 13px 4px 0;
  color: var(--muted);
  font-size: 0.8rem;
  line-height: 1.35;
  text-align: center;
}

.message.is-error {
  color: var(--danger);
  font-weight: 700;
}

.message.is-success {
  color: var(--success);
  font-weight: 750;
}

.controls-card {
  margin-top: 13px;
  padding: 15px 12px calc(14px + var(--safe-bottom));
}

.controls-heading {
  margin: 0 3px 11px;
}

.notes-badge {
  padding: 5px 8px;
  border-radius: 99px;
  background: #f1f4f8;
  color: var(--muted);
  font-size: 0.67rem;
  font-weight: 750;
  white-space: nowrap;
}

.notes-badge.is-on {
  background: var(--accent-soft);
  color: var(--accent-dark);
}

.number-pad {
  display: grid;
  grid-template-columns: repeat(3, minmax(0, 1fr));
  gap: 8px;
}

.number-key {
  min-height: 50px;
  border-radius: 14px;
  background: #fbfcfe;
  box-shadow: 0 2px 3px rgba(31, 53, 86, 0.04);
  color: var(--accent-dark);
  font-size: 1.25rem;
  font-weight: 750;
}

.number-key:active,
.secondary-button:active,
.undo-button:active {
  background: var(--accent-soft);
  transform: translateY(1px);
}

.action-row {
  display: grid;
  grid-template-columns: repeat(2, minmax(0, 1fr));
  gap: 8px;
  margin-top: 9px;
}

.secondary-button {
  justify-content: center;
  gap: 7px;
  min-height: 50px;
  border-radius: 14px;
  background: #fbfcfe;
  font-size: 0.86rem;
  font-weight: 750;
}

.secondary-button.is-on {
  border-color: #b8cff8;
  background: var(--accent-soft);
  color: var(--accent-dark);
}

.action-icon {
  font-size: 1.15rem;
  font-weight: 400;
  line-height: 1;
}

.app-footer {
  padding: 15px 8px 0;
  color: #8b98aa;
  font-size: 0.7rem;
  line-height: 1.35;
  text-align: center;
}

@media (min-width: 430px) {
  .game-card,
  .controls-card {
    padding-left: 16px;
    padding-right: 16px;
  }

  .sudoku-board {
    min-height: 0;
  }
}

@media (min-width: 600px) {
  .app-shell {
    padding-top: calc(34px + var(--safe-top));
  }

  .game-card {
    padding-top: 18px;
  }

  .number-key,
  .secondary-button {
    min-height: 54px;
  }
}

@media (prefers-reduced-motion: reduce) {
  *,
  *::before,
  *::after {
    scroll-behavior: auto !important;
    transition-duration: 0.01ms !important;
    animation-duration: 0.01ms !important;
  }
}