Missing CSS for add-contact link in index.css

In lesson 5, `<a className="add-contact"...` and `<Link className="add-contact"...`  were introduced, but the styles to position this element next to the input field are missing, so the icon is showing up collapsed below the input.

Adding `height: 63px;
  position: absolute;
  top: 0;
  right: 0;` to line 111 of index.css fixes the issue.