:root {
  --face: #c6c6c6;
  --light: #ffffff;
  --shadow: #7b7b7b;
  --dark: #4a4a4a;
  --revealed: #d6d6d6;
  --grid: #b0b0b0;
  --page: #1d2126;
  --ink: #e8eaed;
  --cell: 27px;
}

* { box-sizing: border-box; }

html, body {
  margin: 0;
  padding: 0;
  min-height: 100%;
}

body {
  background: radial-gradient(1200px 600px at 50% -10%, #2a3038, var(--page));
  color: var(--ink);
  font: 15px/1.5 system-ui, -apple-system, "Segoe UI", Roboto, sans-serif;
  display: flex;
  justify-content: center;
  padding: 24px 12px 48px;
  -webkit-text-size-adjust: 100%;
}

.app {
  width: 100%;
  max-width: min(100%, 900px);
  display: flex;
  flex-direction: column;
  align-items: center;
  gap: 16px;
}

.title {
  margin: 0;
  font-size: 26px;
  font-weight: 650;
  letter-spacing: 0.02em;
}

/* ---- difficulty ---- */

.difficulty {
  display: flex;
  gap: 8px;
  flex-wrap: wrap;
  justify-content: center;
}

.diff-btn {
  display: flex;
  flex-direction: column;
  align-items: center;
  gap: 2px;
  padding: 8px 14px;
  border: 1px solid #3a424c;
  border-radius: 8px;
  background: #262c34;
  color: var(--ink);
  font: inherit;
  font-weight: 600;
  cursor: pointer;
  transition: background .12s, border-color .12s;
}

.diff-btn span {
  font-size: 11px;
  font-weight: 400;
  opacity: .6;
  font-variant-numeric: tabular-nums;
}

.diff-btn:hover { background: #2f3742; }

.diff-btn[aria-pressed="true"] {
  background: #3d4a5a;
  border-color: #6f8bb0;
}

/* ---- frame ---- */

.frame {
  background: var(--face);
  padding: 8px;
  border-radius: 4px;
  border-top: 3px solid var(--light);
  border-left: 3px solid var(--light);
  border-right: 3px solid var(--shadow);
  border-bottom: 3px solid var(--shadow);
  max-width: 100%;
}

.hud {
  display: flex;
  align-items: center;
  justify-content: space-between;
  gap: 10px;
  padding: 6px 8px;
  margin-bottom: 8px;
  background: var(--face);
  border-top: 2px solid var(--shadow);
  border-left: 2px solid var(--shadow);
  border-right: 2px solid var(--light);
  border-bottom: 2px solid var(--light);
}

.readout {
  min-width: 58px;
  padding: 2px 6px;
  background: #1a0000;
  color: #ff3b30;
  font-family: ui-monospace, "SF Mono", Menlo, Consolas, monospace;
  font-size: 24px;
  font-weight: 700;
  letter-spacing: 2px;
  text-align: center;
  font-variant-numeric: tabular-nums;
  border: 1px solid #000;
  text-shadow: 0 0 6px rgba(255, 59, 48, .55);
}

.face {
  width: 40px;
  height: 40px;
  font-size: 22px;
  line-height: 1;
  cursor: pointer;
  background: var(--face);
  border-top: 3px solid var(--light);
  border-left: 3px solid var(--light);
  border-right: 3px solid var(--shadow);
  border-bottom: 3px solid var(--shadow);
  display: flex;
  align-items: center;
  justify-content: center;
  padding: 0;
}

.face:active {
  border-color: var(--shadow) var(--light) var(--light) var(--shadow);
}

/* ---- board ---- */

.board-wrap {
  max-width: 100%;
  overflow-x: auto;
  border-top: 3px solid var(--shadow);
  border-left: 3px solid var(--shadow);
  border-right: 3px solid var(--light);
  border-bottom: 3px solid var(--light);
}

.board {
  display: grid;
  gap: 0;
  background: var(--grid);
  width: max-content;
  touch-action: manipulation;
  user-select: none;
  -webkit-user-select: none;
  -webkit-tap-highlight-color: transparent;
}

.cell {
  width: var(--cell);
  height: var(--cell);
  display: flex;
  align-items: center;
  justify-content: center;
  font-family: ui-monospace, "SF Mono", Menlo, Consolas, monospace;
  font-size: calc(var(--cell) * 0.62);
  font-weight: 700;
  line-height: 1;
  cursor: pointer;
  background: var(--face);
  border-top: 3px solid var(--light);
  border-left: 3px solid var(--light);
  border-right: 3px solid var(--shadow);
  border-bottom: 3px solid var(--shadow);
}

.cell.revealed {
  background: var(--revealed);
  border: 1px solid var(--grid);
  cursor: default;
}

.cell.flagged { cursor: pointer; }

.cell.mine-hit { background: #e53935; }

.cell.mine-wrong { color: #b00020; }

.cell.n1 { color: #1976d2; }
.cell.n2 { color: #2e7d32; }
.cell.n3 { color: #d32f2f; }
.cell.n4 { color: #512da8; }
.cell.n5 { color: #8d4b00; }
.cell.n6 { color: #00838f; }
.cell.n7 { color: #212121; }
.cell.n8 { color: #616161; }

.board.over .cell { cursor: default; }

/* ---- footer ---- */

.status {
  margin: 0;
  min-height: 1.5em;
  font-size: 14px;
  opacity: .85;
  text-align: center;
}

.status.win { color: #6ee7a0; opacity: 1; font-weight: 600; }
.status.lose { color: #ff8a80; opacity: 1; font-weight: 600; }

.help {
  max-width: 520px;
  font-size: 13px;
  opacity: .8;
}

.help summary { cursor: pointer; }
.help ul { margin: 8px 0 0; padding-left: 20px; }
.help li { margin: 3px 0; }

@media (max-width: 640px) {
  :root { --cell: 24px; }
  .title { font-size: 22px; }
}