Acknowledging a Subscription Signup

Very new at this, and appreciate the wonderful feedback I'm getting here.

On our CONTACT US page, we have a field for people to subscribe to the mailing list.

Once they input their address, the entire block disappears, and the user is left on the contact page, with that entire area having gone blank.  The words "thank you" then appear under an image.  

To be honest, I came here to ask how to get "Thank You" to appear, because it's taken me four times to realize that they do in fact appear.  But, it's not obvious.

Is there a way to make it bigger, bolder, and move the message by a bit?

Thank you -