How to implement a custom theme for

I'm trying to build a video player based on I downloaded the library and used it to display a simple video element on my page. I want to manipulate the styling of the video controls. I don't want to add custom controls. I want to just change a few props of the default controls provided by the library. Is there anyway to do this by writing a custom sass? I compiled the sass files provided by the dev but including the output css files is messing up the ui a little bit. Any help would be appreciated. :)