I need to customize the PopUp Pro CTA CSS

I'm having trouble customizing the PopUp Pro CTA CSS on this page: http://alaniznew.staging.wpengine.com/blog/5-great-pr-tips-digital-marketing/. It appears when the mouse leaves the browser window. I need to make the green CTA full-width. How do I accomplish this? I haven't been able to target it correctly so far.