Unity gray?

Hi, I installed Unity on my laptop.

After a few minutes playing around and experimenting, I changed something a bit.

In the picture you can see that my surface with the individual objects is gray. I would really like to have this blue - gray background again. In addition, the main camera and the directional light no longer have any texture and (if I'm lucky) are only displayed as a circle.

How can I reset this again?

PS: I've already tried Ctrl + Z.

Turn this on.

And check the camera.