CSS Box ModelOpen image in new window
When viewing the source HTML code of a page, it’s readily apparent that the content is separated using HTML tags. Paragraphs of text are surrounded by <p> and </p> tags, the main navigational menu is surrounded by <nav> and </nav> tags, and so forth. The HTML is defining what content is nested inside what other content on the page—it’s defining the content’s structure. It’s like a rough sketch of the layout of a house, which shows what rooms go where but doesn’t indicate their exact dimensions, color, or other properties of their appearance. The task of describing the appearance of a web page is left to the domain of CSS.