What is this piece on the roof of the vehicle?

[alextlee]

Hello all.
Hopefully you guys can help me identify this part. It's have a gap. I think the plastic piece is loose that's holding it. May need to take it apart and see If I can tighten it up bit versus replacing the whole thing. Any help is greatly appreciated. Thank you.

 

[warrenw]

There are 5 or so nuts on the underside of that center brake trim that can come loose. There was a service bulletin for the center brake lamp in some early cars. If the dealer doing the replacement did not use some thread locker on the nuts, they can come loose. I believe M5. Open the hatch, you will see them. Be careful not to over tighten. You will misshape the trim.

 

[alextlee]

Thanks Warren it's exactly what I need