Correct/Incorrect Pop-Up Box Changes

I am wondering if there is a way to get rid of that little line that goes across the top of the pop-up window.  I have edited my feedback to say something like, "B is the best answer.  Click continue to read more." I do not want this little line on the window though.  I know it's small, but I was wondering if there's a way to get rid of it.

(I went through all my slides that had the pop-ups and put a blue box over them (to hide the line) and then wrote my text...but it messed up my layers on other slides!)

I've included an attachment here so you can see what I'm talking about.  :)  Thanks!!