<html>
<script>
function changeBackground() {
  const color = location.hash.substr(1);
  document.body.style.backgroundColor = color;
}
</script>
<style>
body {
  margin: 0;
}

.container {
  display: grid;
  background-color: rgb(0, 0, 0);
  grid-template-columns: auto auto;
  width: 100%;
  height: 100%;
}

.cell {
  border: none;
  font-size: 30px;
  text-align: center;
}

.cell.grey {
  background-color: rgb(100, 100, 100);
}

.cell.red {
  background-color: rgb(255, 0, 0);
}
</style>
<body>
<div class="container">
  <div class="cell red"></div>
  <div class="cell grey"></div>
  <div class="cell grey"></div>
  <div class="cell red"></div>
</div>
</body>
</html>