As a lib user I would like to see a better typing in the most used functions

[impe93]

What

Good typing in the return type of s() function, which is one of the most important functions for the user. This function should show the possibles classes that the library offer (the default one and not the customizations) and should have a correct return type too.

Why

The function s(), at the moment, gets strings as parameters and returns any. In this way, we cannot prevent the user to wrongly type some classes and the user doesn't get any suggestions about the supported classes. About the return type user, at the moment, cannot understand if the returned style is supported by the element where the style is applied.