.container
  .main main
  .sub sub
View Compiled
.container {
  display: flex;
  justify-content: space-between;
  width: 90%;
  max-width: 1000px;
  margin: 0 auto;
}
.sub {
  background-color: gray;
  width: 300px;
}
.main {
  background-color: gray;
  flex: 1;
  margin-right: 30px;
}
View Compiled

External CSS

This Pen doesn't use any external CSS resources.

External JavaScript

This Pen doesn't use any external JavaScript resources.