This stylesheet should be saved as colour-style.css for Exercise 5:

div.cblock {
  width: 4em;
  height: 2em;
  border: 1px solid black;
}
#a {
  background-color: #000;
}
#b {
  background-color: #000;
}
#c {
  background-color: #000;
}
#d {
  background-color: #000;
}
#e {
  background-color: #000;
}
#f {
  background-color: #000;
}