Submit Button – style override

Hi,
Great plugin. Just wondering how I can fix the ‘submit’ button CSS.

It looks like it’s using the over state CSS rather than the default for my theme – which is white on white (can’t read ‘submit’ text).

http://sentis.com/ (Scroll to bottom).

Other submit buttons: http://sentis.com/contact-us/

Thanks,
Luke

https://ww.wp.xz.cn/plugins/mailchimp-wp/