Install from Greasy Fork.
Need Violentmonkey to work with.
This file is a pure CSS theme that can be applied as a Mastondon custom theme, in which way getting back top navigation bar without a browser extension is possible. It does a similar thing as script.js but has more limitations (both visually and functionally) due to the nature of CSS (alone with the poor coding of the project it applies to).
You don't need to use the script together with it, actually by applying the script, what has been changed in it will mostly get removed.
topbar.css but navbar is on the bottom.
Mastodon founder Eugen Rochko and his highly respected "professional designer" who provided the chance for this script.
The owner of the project knows nothing about JavaScript or CSS. All the codes are written by a monkey who breaches into their room regularly. The owner will try their best to transfer the needs of the users to the monkey, but no guarantees nor warranties will be provided.