Omit core.min.css and use own CSS for hidden class?

Hi!
I have a dropdown and a text filter and it works fine. But the core.min.css renders my text input quite unfortunately.

When I omit the core.min.css almost everything is fine, but

1. the "No results" DIV is always visible
2. and if nothing matches the filter the .list-items won't be hidden

Do I have to just include some classes in my own CSS file or can I set a config for my own class (of the CSS framework perhaps)