:root {
  --cell-size: 50px;
}

* {
  box-sizing: border-box;
  margin: 0;
  padding: 0;
}

body {
  font-family: Arial, sans-serif;
  text-align: center;
  padding: 20px;
}

#board-wrapper {
  display: inline-block;
  margin-top: 18px;
}

#board {
  display: grid;
}

/* chaque case a une bordure de 4px gris clair */
.cell {
  width: var(--cell-size);
  height: var(--cell-size);
  display: flex;
  align-items: center;
  justify-content: center;
  font-size: 32px;
  background: white;
  border: 4px solid #ddd; /* gris clair */
}