When it comes to web standards, something is always mentioned, that is, the importance of the separation of structure and presentation.
Understanding the differences between structure and presentation can be difficult at first, especially if you’re not used to thinking about the semantic structure of a document.
However, it is important to understand this, because when the structure and presentation are separated, it is easy to control the presentation with CSS documents.
Structure consists of the main part of the document, plus semantic and structured tags.
Performance is a style you give content. In most cases, presentation is what a document looks like, but it can also affect how a document “sounds” — after all, not everyone uses an image browser.
Separate the structure and performance as much as possible.
In theory, you should use an HTML document to save the content and structure, and a CSS document to control the performance of the whole document.
Nowadays, it is still common for websites that are not separated from structure.