CSS is the mechanism for styling HTML. Almost every example in the book begins with a block of HTML code that I then style with CSS. HTML is shown like this:
HTML ignores all white space, returns, and tabs, except within text, where single spaces are respected, but more than one space is ignored. This gives you options for formatting. For example, these are all equivalents and display: An HTML paragraph element.
CSS is shown like this:
CSS also ignores white space, tabs, and returns, so these are equivalents: ...