Some view frameworks can take out the code of common parts of the page (such as the head and tail) and store it in a new file, and then reference it in each file, such as the ejs view of Node.js and ASP, etc. in this way.

The background framework generally has something similar to the layout page
The same and common layout and style are written in the layout page and sub-page inheritance

This is called a tab page. There are many similar jQuery plug-ins, such as Bootstrap's tab page. It's not clear how to do it

Only write one code for the public part, use ajax to import it as needed, make corresponding judgments when rendering the web page, display the selected status, and it's OK

There are many ways to achieve this effect. You can use the front-end method or the back-end method.
The front end can be introduced by ajax or dynamic template.
The backend can be ssi technology, etc.
Hope this helps.

This kind of thing. . See what it is written in, if it is php, it would be nice to call the unified header.