in my ASP.Net I have following hamburger menu:

<nav class="navbar navbar-expand-sm navbar-toggleable-sm navbar-light bg-white border-bottom box-shadow mb-3">

Besides I am using following project as a switch to switch to dark mode:
https://github.com/coliff/dark-mode-switch -> dark-mode-switch.min.js

This works fine to change buttons etc that are in CSS, but probably I wont be able to use it to change navbar-light to navbar-dark in class.
So I do not know if it has to be done in that JavaScript File mentioned above or if it can be done by CSS as well.
What would be the way to include it into the rest?