html, body {
  height: 100%;
  margin: 0;
  background-color: #000;
}

#overlay {
  position: fixed;
  width: 100%;
  height: 100%;
  background-color: rgba(0, 0, 0, 0.7);
  display: flex;
  align-items: center;
  justify-content: center;
  font-size: 4em;
  font-family: sans-serif;
  color: #fff;
}

#controls {
  height: 100%;
  display: flex;
  flex-direction: column;
  gap: 1em;
  user-select: none;
}

#controls button {
  font-size: 10em;
  display: flex;
  flex: 1;
  justify-content: center;
  align-items: center;
  border-radius: 0;
  border: 0;
  border-top: 1px solid #999;
  border-bottom: 1px solid #999;
  user-select: none;
}

#controls.left button {
  background-color: red;
}

#controls.right button {
  background-color: blue;
}