:root {
  --bg: #f3efe4;
  --panel: rgba(255, 252, 245, 0.94);
  --line: #53473b;
  --line-soft: rgba(83, 71, 59, 0.18);
  --accent: #2b6b5f;
  --accent-strong: #1f4b43;
  --danger: #a64237;
  --text: #231f1a;
  --muted: #6d645c;
  --board-size: min(41rem, calc(100vw - 2rem));
  --shadow: 0 18px 45px rgba(52, 40, 25, 0.16);
  font-family: "Trebuchet MS", "Segoe UI", sans-serif;
}

* {
  box-sizing: border-box;
}

body {
  margin: 0;
  min-height: 100vh;
  color: var(--text);
  background:
    radial-gradient(circle at top, rgba(255, 255, 255, 0.8), transparent 32%),
    linear-gradient(160deg, #e7dfcf 0%, #f7f4eb 48%, #ece3d3 100%);
}

button {
  font: inherit;
}

.app {
  width: min(100%, 66rem);
  margin: 0 auto;
  padding: 1rem;
}

.workspace {
  display: grid;
  gap: 1rem;
}

.eyebrow {
  margin: 0 0 0.4rem;
  color: var(--accent-strong);
  font-size: 0.8rem;
  font-weight: 700;
  letter-spacing: 0.16em;
  text-transform: uppercase;
}

.controls-heading h1 {
  margin: 0;
  font-size: clamp(1.8rem, 3vw, 2.45rem);
  line-height: 1;
}

.controls-heading {
  margin-bottom: 1.1rem;
  text-align: center;
}

.board-panel,
.controls {
  background: var(--panel);
  border: 1px solid rgba(83, 71, 59, 0.08);
  border-radius: 1.3rem;
  box-shadow: var(--shadow);
  backdrop-filter: blur(14px);
}

.board-panel {
  padding: 1rem;
}

.status-row,
.action-row {
  display: flex;
  gap: 0.75rem;
  align-items: center;
  justify-content: space-between;
}

.status-row {
  margin-bottom: 1rem;
}

.status {
  margin: 0;
  color: var(--muted);
  min-height: 1.5rem;
}

.action-button,
.pad-button {
  border: 0;
  border-radius: 1rem;
  cursor: pointer;
  transition: transform 120ms ease, background-color 120ms ease, color 120ms ease;
}

.action-button:hover,
.pad-button:hover,
.action-button:focus-visible,
.pad-button:focus-visible {
  transform: translateY(-1px);
}

.action-button:disabled,
.pad-button:disabled {
  cursor: wait;
  opacity: 0.62;
  transform: none;
}

.board {
  display: grid;
  grid-template-columns: repeat(9, minmax(0, 1fr));
  grid-template-rows: repeat(9, minmax(0, 1fr));
  gap: 0;
  width: var(--board-size);
  height: var(--board-size);
  max-width: 100%;
  max-height: 100%;
  aspect-ratio: 1 / 1;
  margin: 0 auto;
  border: 3px solid var(--line);
  border-radius: 1rem;
  overflow: hidden;
  background: #fffdf8;
}

.cell {
  appearance: none;
  -webkit-appearance: none;
  width: 100%;
  height: 100%;
  min-width: 0;
  min-height: 0;
  padding: 0;
  margin: 0;
  display: grid;
  place-items: center;
  border-right: 1px solid var(--line-soft);
  border-bottom: 1px solid var(--line-soft);
  background: transparent;
  color: var(--text);
  font-size: clamp(1.15rem, 3vw, 2rem);
  font-weight: 800;
}

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

.cell[data-col="2"],
.cell[data-col="5"] {
  border-right: 3px solid var(--line);
}

.cell[data-row="2"],
.cell[data-row="5"] {
  border-bottom: 3px solid var(--line);
}

.cell.related {
  background: rgba(43, 107, 95, 0.08);
}

.cell.selected {
  background: rgba(43, 107, 95, 0.22);
  color: var(--accent-strong);
}

.cell.invalid {
  background: rgba(166, 66, 55, 0.18);
  color: var(--danger);
}

.cell.solved-value {
  color: #0d6b57;
  text-shadow: 0 0 0 rgba(0, 0, 0, 0.01);
}

.cell.user-value {
  color: #1b4f9c;
}

.controls {
  margin-top: 1rem;
  padding: 1rem;
}

.number-pad {
  display: grid;
  grid-template-columns: repeat(3, minmax(0, 1fr));
  gap: 0.75rem;
}

.pad-button,
.action-button {
  min-height: 3.6rem;
  padding: 0.9rem 1rem;
  background: #fffdf8;
  color: var(--text);
  box-shadow: inset 0 0 0 1px rgba(83, 71, 59, 0.12);
  font-size: 1.2rem;
  font-weight: 700;
}

.pad-button-wide {
  grid-column: span 3;
}

.action-row {
  margin-top: 1rem;
}

.action-button {
  flex: 1;
}

.action-button-primary {
  background: var(--accent);
  color: #fffdf8;
  box-shadow: none;
}

.action-button-new {
  background: #1f5f9f;
  color: #fffdf8;
  box-shadow: none;
}

.action-button-hint {
  background: #c76b20;
  color: #fffdf8;
  box-shadow: none;
}

@media (max-width: 720px) {
  :root {
    --board-size: calc(100vw - 2.2rem);
  }

  .app {
    padding: 0.7rem;
  }

  .board-panel,
  .controls {
    border-radius: 1.1rem;
  }

  .board-panel {
    padding: 0.8rem;
  }

  .status-row,
  .action-row {
    flex-direction: column;
    align-items: stretch;
  }

  .status {
    text-align: center;
  }

  .board {
    width: var(--board-size);
    height: var(--board-size);
  }

  .cell {
    font-size: clamp(1.05rem, 5vw, 1.55rem);
  }

  .controls {
    padding: 0.8rem;
  }

  .number-pad {
    gap: 0.55rem;
  }

  .pad-button,
  .action-button {
    min-height: 3.25rem;
    padding: 0.8rem 0.6rem;
    font-size: 1.05rem;
    border-radius: 0.9rem;
  }

  .action-row {
    gap: 0.55rem;
  }

  .pad-button-wide {
    grid-column: span 3;
  }
}

@media (min-width: 820px) and (orientation: landscape) {
  :root {
    --board-size: min(calc(100vh - 3.2rem), calc(100vw - 15rem));
  }

  body {
    overflow: hidden;
  }

  .app {
    width: min(100%, 76rem);
    min-height: 100vh;
    padding: 0.55rem;
    display: grid;
    grid-template-rows: 1fr;
    align-content: center;
  }

  .workspace {
    grid-template-columns: var(--board-size) minmax(11.5rem, 13.5rem);
    align-items: center;
    justify-content: center;
    gap: 0.6rem;
  }

  .board-panel,
  .controls {
    margin: 0;
  }

  .board-panel {
    display: grid;
    grid-template-rows: auto 1fr;
    align-items: center;
    padding: 0.6rem;
    width: calc(var(--board-size) + 1.2rem);
    max-width: 100%;
  }

  .controls {
    display: flex;
    flex-direction: column;
    justify-content: center;
    padding: 0.65rem;
    width: 100%;
  }

  .status-row {
    margin-bottom: 0.45rem;
  }

  .status {
    font-size: 0.9rem;
    min-height: 1rem;
    text-align: center;
  }

  .board {
    border-radius: 0.8rem;
  }

  .controls-heading h1 {
    font-size: clamp(1.35rem, 2.1vw, 1.75rem);
  }

  .controls-heading {
    margin-bottom: 0.65rem;
  }

  .eyebrow {
    margin-bottom: 0.25rem;
    font-size: 0.65rem;
    letter-spacing: 0.13em;
  }

  .number-pad {
    gap: 0.42rem;
  }

  .pad-button {
    min-height: 3rem;
    padding: 0.45rem 0.35rem;
    border-radius: 0.75rem;
    font-size: 1.1rem;
  }

  .action-row {
    flex-direction: column;
    align-items: stretch;
    gap: 0.42rem;
    margin-top: 0.55rem;
  }

  .action-button {
    min-height: 2.75rem;
    padding: 0.5rem 0.45rem;
    border-radius: 0.75rem;
    font-size: 0.98rem;
  }
}

@media (max-width: 430px) {
  :root {
    --board-size: calc(100vw - 1.7rem);
  }

  .app {
    padding-left: 0.55rem;
    padding-right: 0.55rem;
  }

  .board-panel,
  .controls {
    border-radius: 1rem;
  }

  .board-panel {
    padding: 0.65rem;
  }

  .cell {
    font-size: clamp(1rem, 5.4vw, 1.35rem);
  }
}