body {
  display: grid;
  height: 100vh;
  grid-template-columns: repeat(12, 1fr);
}

// etc

div {
  display: grid;
  place-items: center;
}

.span-12 {
  background: lightpink;
  grid-column: 1 / 13;
}

.span-6 {
  background: lightblue;
  grid-column: 1 / 7;
}

.span-4 {
  background: coral;
  grid-column: 4 / 9;
}

.span-2 {
  background: yellow;
  grid-column: 3 / 5;
}

body {
  font-family: system-ui, sans-serif;
}