Too Long; Didn't Read
The advantages of a marvelous layout, semantic markup, and separation of content from design have been already described hundreds of times. Still, there are developers who do not follow the concept of working with HTML and CSS. In the HTML file, we describe only the logical part of the document and nothing of the design. And all styling is on the side of the CSS, and all the design is in a CSS file. The reason not using this approach is all about the ideology of HTML design.