addtocartips it seems like this code will apply in a lot of places in Flarum.
It's best to use the context-specific classes like
.item-<name> and the other special classnames generally added to each control.
Dropdown--select is used in many places by Flarum itself, and it's a re-usable component that many extensions will use for various purposes.
I have not really understood which part of the UI the OP wants to change so I cannot make a recommendation but if we have a screenshot of what part you are trying to target I could share more specific class names.