game.css

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

body {
  height: 100vh;
  width: 100vw;
}

main {
  display: grid;
  grid-template-columns: 1fr 1fr 1fr 1fr;
  height: 100vh;
}

button {
  background-color: white;
  font-size: 2rem;
}