CSS Fix for submit button that's expanding beyond its container?

http://test.breakingtradition.net/traditiongame/

I’m using some contact forms to take input for this game that I’m putting together for a client. So I finally got the game working properly, but there’s some weird CSS glitch with the Contact Form 7 Plugin. I’m having the same problem on another install of wordpress, so I’m pretty sure that the plugin is causing the problem, I’m just not sure how to fix it.

So what happens is, in a full width browser the submit button is a normal size (approx 80px wide), but when you resize the browser, all of a sudden the input button decides to be wider than the div that it’s contained within! I’ve tried specifying a width for the element using the developer tools, but no luck. I think there must be some !important CSS in the plugin? I’m not sure where to look.

Any ideas?

Regards,

Dakota