index.css

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

html, body {
  height: 100%;
  color: white;
  font-family: system-ui, -apple-system, BlinkMacSystemFont, 'Segoe UI', Roboto, Oxygen, Ubuntu, Cantarell, 'Open Sans', 'Helvetica Neue', sans-serif;
  font-size: calc(1em + .3vh);
}

header {
  display: flex;
  justify-content: space-evenly;
  gap: 1em;
  margin: 3em 0em;
}

h1 {
  font-size: 1.3em;
}

body {
  background-color: black;
  display: flex;
  flex-direction: column;
  align-items: center;
  
  overscroll-behavior: none;
}

#board {
  height: 88vw;
  width: 88vw;

  max-width: 500px;
  max-height: 500px;

  border: 1px solid white;
  position: relative;
}

#timer, #score, #highScore {
  color: white;
}

.snakeSquare, #apple {
  display: block;
  width: 4%;
  height: 4%;
  position: absolute;
  user-select: none;
}

.snakeSquare {
  background-color: green;
  z-index: 2;
}

#snake-head {
  background-color: darkgreen;
}

#apple {
  background-color: red;
  z-index: 1;
}