CSS, or Cascading Style Sheets, defines the look and formatting of that HTML. Both are essential to coding your own website, and here's how to get acquainted with them.

Your takeaways This course is a great way to help you: • Create HTML5 code, CSS style sheets and embedded styles within HTML5 code. • Create responsive page layouts for both mobile and desktop use; • ...

Make sure you validate your HTML and CSS, using a service like the W3C’s validator. This will warn you about obsolete tags and other errors that may make your HTML less robust.