How to "X Out" a strip?

I know, I could just do a lightbox, but I’d like to put a red strip right under the header with a notice that can be x-ed out, or closed. My hope would be that it would then disappear and everything below it would move up to close the gap, similar to what would happen if you had a collapse button–but instead of partially disappearing, everything would…

So should I take some code that collapses a strip and try to modify it, or should I try to start from scratch (being trying to find code for that somewhere, since I have absolutely no idea how to do it)?

I really don’t know what to do, I did some research, but no one anywhere seemed to know how to do it, or I just didn’t search with the right words.

Any recommendations for me?