:root {
  --bg: #0b1220;
  --panel: #111a2e;
  --text: #e7eefc;
  --muted: #a8b3cc;
  --accent: #7aa2ff;
  --danger: #ff6b6b;
  --cell: #0f1830;
  --cellHover: #152248;
  --border: rgba(231, 238, 252, 0.14);
}

* {
  box-sizing: border-box;
}

body {
  margin: 0;
  font-family: system-ui, -apple-system, Segoe UI, Roboto, Ubuntu, Cantarell, Noto Sans,
    sans-serif;
  background: radial-gradient(1000px 600px at 20% 10%, rgba(122, 162, 255, 0.22), transparent),
    radial-gradient(900px 600px at 90% 10%, rgba(255, 107, 107, 0.12), transparent), var(--bg);
  color: var(--text);
  min-height: 100vh;
  display: grid;
  place-items: center;
  padding: 24px;
}

.app {
  width: min(520px, 100%);
  display: grid;
  gap: 16px;
}

.header-content {
  display: flex;
  align-items: center;
  gap: 12px;
}

.back-button {
  flex-shrink: 0;
  width: 36px;
  height: 36px;
  display: flex;
  align-items: center;
  justify-content: center;
  background: var(--panel);
  border: 1px solid var(--border);
  border-radius: 8px;
  color: var(--muted);
  text-decoration: none;
  transition: all 0.2s ease;
}

.back-button:hover {
  background: var(--cellHover);
  border-color: var(--accent);
  color: var(--accent);
  transform: translateX(-2px);
}

.back-button:active {
  transform: translateX(-2px) scale(0.95);
}

.header h1 {
  margin: 0;
  font-size: 28px;
  letter-spacing: 0.4px;
  line-height: 1;
  padding: 0;
}

.subtitle {
  margin: 8px 0 0;
  color: var(--muted);
  font-size: 14px;
}

.mode-selector {
  display: flex;
  gap: 8px;
  background: var(--panel);
  border: 1px solid var(--border);
  padding: 8px;
  border-radius: 12px;
}

.mode-btn {
  flex: 1;
  appearance: none;
  border: 1px solid transparent;
  background: transparent;
  color: var(--muted);
  font-size: 14px;
  font-weight: 500;
  padding: 10px 16px;
  border-radius: 8px;
  cursor: pointer;
  transition: all 0.2s ease;
}

.mode-btn:hover {
  background: var(--cellHover);
  color: var(--text);
}

.mode-btn.active {
  background: var(--accent);
  color: var(--bg);
  border-color: var(--accent);
}

.difficulty-selector {
  display: flex;
  gap: 8px;
  background: var(--panel);
  border: 1px solid var(--border);
  padding: 8px;
  border-radius: 12px;
}

.difficulty-btn {
  flex: 1;
  appearance: none;
  border: 1px solid transparent;
  background: transparent;
  color: var(--muted);
  font-size: 13px;
  font-weight: 500;
  padding: 8px 12px;
  border-radius: 8px;
  cursor: pointer;
  transition: all 0.2s ease;
}

.difficulty-btn:hover {
  background: var(--cellHover);
  color: var(--text);
}

.difficulty-btn.active {
  background: var(--danger);
  color: white;
  border-color: var(--danger);
}

.panel {
  background: var(--panel);
  border: 1px solid var(--border);
  padding: 16px;
  border-radius: 12px;
  display: flex;
  align-items: center;
  justify-content: space-between;
  gap: 12px;
}

.status {
  font-weight: 600;
}

.btn {
  appearance: none;
  border: 1px solid var(--border);
  background: transparent;
  color: var(--text);
  padding: 10px 16px;
  border-radius: 10px;
  cursor: pointer;
  font-size: 14px;
}

.btn:hover {
  border-color: rgba(122, 162, 255, 0.6);
}

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

.board {
  background: var(--panel);
  border: 1px solid var(--border);
  border-radius: 16px;
  padding: 14px;
  display: grid;
  grid-template-columns: repeat(3, 1fr);
  gap: 10px;
}

/* En tu HTML las celdas están dentro de <div role="row">.
   Esto hace que esos wrappers no rompan el grid visual. */
.board > div {
  display: contents;
}

.cell {
  height: clamp(84px, 18vw, 130px);
  border-radius: 14px;
  border: 1px solid var(--border);
  background: var(--cell);
  color: var(--text);
  font-size: clamp(34px, 7vw, 54px);
  font-weight: 800;
  cursor: pointer;
  display: grid;
  place-items: center;
  transition: background 0.2s;
  -webkit-user-select: none;
  user-select: none;
}

.cell:hover {
  background: var(--cellHover);
}

.cell:focus-visible {
  outline: 2px solid rgba(122, 162, 255, 0.75);
  outline-offset: -2px;
}

.cell:disabled {
  cursor: not-allowed;
  opacity: 0.92;
}

.cell.x {
  color: var(--accent);
}

.cell.o {
  color: var(--danger);
}

.cell.win {
  outline: 2px solid rgba(122, 162, 255, 0.75);
  outline-offset: 2px;
}

.footer {
  color: var(--muted);
  text-align: center;
  font-size: 13px;
  margin-top: 8px;
}