Thank you for your reply. I am confused about how the theme style is overriding the plugin style for the button, though, if you wouldn't mind elaborating a little to help me.
Here is my theme's default style for a contact page (however, I am not using their contact page template, but am using a plain full-width page w/ contact form 7 plugin, instead): http://demo.themezilla.com/classica/contact/
And here is my contact 7 form: http://ciampacreative.com/testing/contact/
So I am not seeing how the Classica theme button would be overriding the contact form 7 button. I'm not sure what's happening! Any thoughts? I would greatly appreciate it!!