change sumbit button colors

Hello,
I’m using a Twenty Eleven child theme and can’t figure out how to change the color of my “submit” button. To see what I am talking about, please refer to:
https://www.lethalamounts.com/dev/

You can see the “subscribe” button on my sidebar in the mailing list widget. I know it has something to do with my theme’s css because it’s also affecting another section of the website:
https://www.lethalamounts.com/dev/store/shop/

Please let me know if you have a solution!

Many thanks.