Margin and padding are your friends.
When you're building a website, some space means your site looks light, easy to read, relaxed and inviting.
I've used:
- box-sizing:border-box so the elements don't pay attention to border or padding when determining their width (important when working with percentages)
- used 20px of padding inside the elements
- added margin to the bottom and left of the aside (blue box with text)
- and all text elements are set to a line height of 1.4.