Which plugin to use for the menu on the left?

Question

css

Hello. There is a side menu, if the page is very long, then after it goes down there will be just a menu background, without navigation. Tell me how to make the navigation also go.
This doesn't fit:

#menu {
      position: fixed;
}

After all, if the resolution is small, then half of the menu will disappear from view.
There is a theme on WordPress where this is implemented: deone.ru
Tell me , are there any plugins? Thank you.

Answer 1

So very difficult to understand. Please provide the html code of the page and css. Then it will be clearer, and so, the code you provided should work.

Answer 2

Your example just goes position: fixed;
Only applies when the menu's offsetTop becomes 0
In the file look for function scroll()

Answer 3

If you send me a link to the site, I will help

Answer 4

a bunch of them) for example https://slideout.js.org/