Plugin Car Demons search button

How can I change colors on the Search button of the form SEARCH of the Car Demons plugin? It is on the spanish version.

If you see the page http://www.autosejercito.com/ and click on the action button, you will be taken to the search form. You can barely see the search button in the lower right hand corner of the widget because it has white letters on a very light gray background. THIS IS WHAT I WANT TO CHANGE TO MAKE IT VISIBLE.

How to do it?

I’ll appreciate any suggestions.