Style upload button

Hi,

I’m trying to find a way to style three upload buttons I’ve put on one of my contact forms.
I know my way around CSS, but I can’t seem to target the buttons. When I open up the developer tools in Chrome, there a list of user agent stylesheets, but I can’t change them to see what happens and when I try to target one of the classes that are shown, nothing happens.

Perhaps I’m missing something, but I hope somebody can give me a hand.

This is the page where the buttons are: https://www.brandmannen.nl/upload and there’s three buttons called “Bestand kiezen” I would like to customize.

Thanks in advance!

– Wouter

https://www.ads-software.com/plugins/contact-form-7/