Widget – the email input section is too long!

My page is at http://thefalliblegirl.com.

The issue is obvious (well to me) – the Notifications widget, which is the Sendpress subscription widget, has too long an email insert button. I would like the whole border to be shown. I have no idea what file to fix here…sorry, still new…any help would be MOST appreciated!

Thanks!

http://wordpress.org/extend/plugins/sendpress/