* {
  box-sizing: border-box;
  margin: 0;
  padding: 0;
}
body {
  font-family: Arial, sans-serif;
  display: flex;
  align-items: center;
  justify-content: center;
  height: 100vh;
  background-color: #f5f5f5;
}
.container {
  text-align: center;
}
.board {
  display: grid;
  grid-template-columns: repeat(3, 1fr);
  gap: 5px;
  margin: 20px auto;
  width: 90vw;
  max-width: 300px;
}
.cell {
  background-color: #fff;
  display: flex;
  align-items: center;
  justify-content: center;
  font-size: 2rem;
  min-height: 60px;
  cursor: pointer;
}
.cell.disabled {
  pointer-events: none;
  color: #888;
}
#message {
  margin-top: 10px;
  min-height: 1.5em;
}
#restart {
  margin-top: 10px;
  padding: 8px 16px;
}