How do I add a border to the Text field?

I want to add a black border to the text field in my form so it will be more noticeable.  Can this be done and how? 

Thank you.

Thank you, that did help and was successful. What if I only want the border around one text field and not both that are present in the form? Is it possible to do that?

Thank you very much!! You were very helpful!  It worked!