Confirm Payment button barely visible. What is the easiest way to customize this button?

http://imgur.com/qifkrzH
Above is a link to what I'm seeing. As you see the confirm payment button that pops up is barely visible. I'm not sure if the way it looks was intentional or some issue with it and my site but either way I definitely want to make it more visible. What would you recommend for the easiest way to customize this button?

I saw in someone else's question, I believe someone recommended to add:
.app_submit_btn{ background: red !important:}
to the Additional CSS Rules section.
I tried and cleared my cache but that didn't work.
I know my way around code and wordpress to a decent extent but this has me slightly stumped. Any help will be GREATLY appreciated.

Thank you!