breebrouwer on "Wysija Newsletters: centering"

Hey, everyone,

I'm trying to center my Wysija sign-up form on this page:
http://geekmylife.net/free-ebook-superhero-drinks

I cannot for the life of me get this centered. The form won't center when I use the Wordpress page editor to center the form and text around it. The text will center, but the form won't.

I tried this fix to my theme's style.css file that others said worked for them to center the submit button (at the very least):

.form-valid-sub input[type="submit"] {
	margin-left:auto;
	margin-right:auto;
}

But this didn't do anything.

Any suggestions? If you provide me css coding please tell me exactly which file to put it in if you want me to put it in a Wysija stylesheet as opposed to my theme's style.css file.

Thanks!