If you look at the code for this page (right-click and choose "View Source"), you'll see
that some HTML elements have an ID associated with it, and those properties are defined in the <style> section at the top of the document. Also notice that a selector can have an ID and a Class at the same time.
You can easily change the appearance of this page by tweaking the CSS values at the top of this document,
saving, and reloading the page.