I see that others have suggested this before, so I have done a copy and paste below of a previous post.  I think this would be a nice feature to have and hope that you will be adding it soon.  It just doesn't look very nice to have buttons throughout a website in one colour and size and then the contact form button to be different.   Thank you for your attention to this matter! 

"Currently the contact form only offers one button style option while all other buttons offer two styles. It would be nice to have both button style options. Otherwise the contact form "submit" button is inconsistent with the others."