:root {
  --bg-top: #eef2eb;
  --bg-bottom: #d7e4ed;
  --surface: rgba(255, 255, 255, 0.88);
  --surface-strong: #ffffff;
  --surface-muted: #f4f7f2;
  --line: #8ea2ad;
  --line-strong: #40515a;
  --accent: #1d7f7a;
  --accent-deep: #15504f;
  --accent-soft: #d7f2ee;
  --player: #215f91;
  --warning: #c96a22;
  --danger: #b53a3a;
  --danger-soft: #ffe8e4;
  --text-main: #21343c;
  --text-soft: #5b727b;
  --shadow-lg: 0 24px 60px rgba(31, 55, 64, 0.14);
  --radius-lg: 26px;
  --radius-sm: 12px;
}

* {
  box-sizing: border-box;
}

html {
  font-size: 16px;
}

body {
  margin: 0;
  min-height: 100vh;
  font-family: "Trebuchet MS", "Gill Sans", Tahoma, sans-serif;
  color: var(--text-main);
  background:
    radial-gradient(circle at top left, rgba(29, 127, 122, 0.14), transparent 28%),
    radial-gradient(circle at top right, rgba(33, 95, 145, 0.14), transparent 26%),
    linear-gradient(180deg, var(--bg-top), var(--bg-bottom));
}

button {
  font: inherit;
}

.app-shell {
  width: min(100vw - 1rem, 100%);
  margin: 0 auto;
  padding: 0.75rem 0 calc(1.5rem + env(safe-area-inset-bottom));
}

.hero-card,
.board-panel,
.pad-panel {
  background: var(--surface);
  border: 1px solid rgba(64, 81, 90, 0.12);
  border-radius: var(--radius-lg);
  box-shadow: var(--shadow-lg);
  backdrop-filter: blur(14px);
}

.hero-card {
  position: relative;
  z-index: 20;
  padding: 0.4rem 1rem;
}

h1 {
  margin: 0;
  font-family: Georgia, "Times New Roman", serif;
  font-size: clamp(1.8rem, 6.4vw, 2.35rem);
  line-height: 0.98;
}

.button-row {
  display: grid;
  gap: 0.7rem;
  grid-template-columns: repeat(2, minmax(0, 1fr));
}

.button-row button,
.pad-button {
  border: 1px solid rgba(64, 81, 90, 0.16);
  border-radius: var(--radius-sm);
  background: var(--surface-strong);
  color: var(--text-main);
  transition:
    transform 160ms ease,
    border-color 160ms ease,
    box-shadow 160ms ease,
    background-color 160ms ease;
}

.button-row button,
.pad-button {
  min-height: 3.25rem;
  padding: 0.8rem 0.9rem;
  font-weight: 700;
  cursor: pointer;
  touch-action: manipulation;
}

.button-row button:hover,
.button-row button:focus-visible,
.pad-button:hover,
.pad-button:focus-visible {
  outline: none;
  border-color: rgba(29, 127, 122, 0.58);
  box-shadow: 0 0 0 4px rgba(29, 127, 122, 0.12);
  transform: translateY(-1px);
}

.button-row button:active,
.pad-button:active {
  transform: translateY(0);
}

.button-row button:disabled,
.pad-button:disabled,
.cell:disabled {
  cursor: not-allowed;
  opacity: 0.68;
  transform: none;
  box-shadow: none;
}

#newPuzzleBtn {
  background: linear-gradient(135deg, #ddf7f3, #effbf9);
}

#checkPuzzleBtn {
  background: linear-gradient(135deg, #fff4e7, #fff9f2);
}

#undoActionBtn {
  background: linear-gradient(135deg, #eef2f7, #f7f9fc);
}

.game-card {
  position: relative;
  z-index: 1;
  display: grid;
  gap: 0.9rem;
  margin-top: 0.9rem;
}

.board-panel,
.pad-panel {
  display: grid;
  gap: 0.85rem;
}

.board-panel {
  padding: 0;
}

.pad-panel {
  padding: 0.85rem;
}

.board {
  display: grid;
  grid-template-columns: repeat(var(--board-size, 9), minmax(0, 1fr));
  width: 100%;
  max-width: var(--board-max-width, 620px);
  min-width: min(100%, var(--board-min-width, 0px));
  margin: 0 auto;
  aspect-ratio: 1;
  background: var(--surface-strong);
  border: 3px solid var(--line-strong);
  border-radius: 18px;
  overflow: hidden;
}

.cell {
  position: relative;
  display: grid;
  place-items: center;
  border: 1px solid rgba(64, 81, 90, 0.16);
  background: rgba(255, 255, 255, 0.96);
  color: var(--player);
  font-size: var(--cell-font-size, 1.5rem);
  font-weight: 700;
  line-height: 1;
  aspect-ratio: 1;
  cursor: pointer;
  user-select: none;
  transition:
    background-color 130ms ease,
    color 130ms ease,
    transform 130ms ease,
    box-shadow 130ms ease;
}

.cell:hover,
.cell:focus-visible {
  outline: none;
  background: #f3faf8;
}

.cell.border-right {
  border-right-width: 3px;
  border-right-color: var(--line-strong);
}

.cell.border-bottom {
  border-bottom-width: 3px;
  border-bottom-color: var(--line-strong);
}

.cell.is-fixed {
  background: #edf2ea;
  color: var(--accent-deep);
  font-weight: 800;
}

.cell.is-filled {
  color: var(--player);
}

.cell.is-peer {
  background: #eef7fb;
}

.cell.is-same-value {
  background: #e6f4fd;
}

.cell.is-selected {
  background: linear-gradient(180deg, #d9f2ef, #cde8f5);
  color: #0f394f;
  box-shadow: inset 0 0 0 3px rgba(29, 127, 122, 0.3);
  transform: scale(0.98);
}

.cell.is-incorrect {
  background: #fff1e4;
  color: var(--warning);
}

.cell.is-conflict {
  background: var(--danger-soft);
  color: var(--danger);
  box-shadow: inset 0 0 0 3px rgba(181, 58, 58, 0.22);
}

.number-pad {
  display: grid;
  grid-template-columns: repeat(var(--pad-columns, 3), minmax(0, 1fr));
  gap: 0.65rem;
}

.pad-button {
  min-height: 3.15rem;
  font-size: 1.1rem;
}

.pad-button[data-action="clear"] {
  background: linear-gradient(135deg, #fff2f0, #fff8f7);
}

.pad-button[data-action="undo"] {
  background: linear-gradient(135deg, #eef2f7, #f7f9fc);
  font-size: 0.98rem;
}

.finish-summary {
  display: grid;
  gap: 0.25rem;
  padding: 0.85rem 0.9rem;
  border-radius: var(--radius-sm);
  background: linear-gradient(135deg, #edf8f6, #f4fbff);
  border: 1px solid rgba(29, 127, 122, 0.16);
}

.finish-summary[hidden] {
  display: none;
}

.finish-label {
  font-size: 0.74rem;
  font-weight: 700;
  letter-spacing: 0.08em;
  text-transform: uppercase;
  color: var(--text-soft);
}

.finish-summary strong {
  font-size: 1.35rem;
  line-height: 1.1;
  color: var(--accent-deep);
}

@media (min-width: 720px) {
  .app-shell {
    width: min(100vw - 1.5rem, 100%);
    padding-top: 1rem;
  }

  .hero-card,
  .pad-panel {
    padding: 1rem;
  }

  .board-panel {
    padding: 0;
  }

  h1 {
    font-size: clamp(2.3rem, 5vw, 3rem);
  }
}

@media (min-width: 980px) {
  .app-shell {
    width: min(1180px, calc(100vw - 2.5rem));
    padding-bottom: 2rem;
  }

  .game-card {
    grid-template-columns: minmax(0, 1fr) 320px;
    align-items: start;
  }

  .pad-panel {
    position: sticky;
    top: 1rem;
  }
}