body{
  padding: 24px;
}
section{
  padding: 16px;
  background-color: lightgray;
  margin: 1em;
  padding: 1em;
}
.blue, .red{
  height: 200px;
  line-height: 200px;
  font-size: 1.4em;
  text-align: center;
  color: white;
}
.blue{
  float: left;
  width: 200px;
  background-color: slateblue;
}
.red{
  float: left;
  width: calc(100% - 200px);
  background-color: tomato;
}