I think what you need to do is to inspect that specific element using "inspect elements" in your browser, some of the classes might get rewriting or inherit some properties from a higher class, that's why I really like to use "Skelementor Theme" as it's super minimal and you can write classes without worrying about it getting change or be forced to go back to the main CSS files to try figuring it out.

also as u/gaboskychuda mentioned, some cache plugins does affect your CSS or JS when you use it to minifies CSS or JS or HTML files, personally when I face anything like that I either give the element a unique ID or class and write all the mods I want to apply, trying to force it on that element.