How can I delete this feature?

[Nichrome]

I don't know how I ended up here but I can't remove this grey page that appears when I change tabs. I have looked at Safari settings but there are literally 8 options and non of them is about this grey page that suddenly pops up. Do you know how I can delete it? It used to go away when I clicked somewhere else but now it just doesn't go away and I can't check my emails!
Also I can't find Clear Cache (and Clear History) in the settings...

 

[Cory Cooper]

Hello and welcome.

-Which model Mac?
-Which version of OS X/macOS?
-Which version of Safari?
-Do you have any other browsers installed like Google Chrome? If so, do they have the same issue?
-Can you upload a screenshot or photo, so we can see what you are seeing?

You can clear history in Safari by clicking Safari > Clear History in the menu bar.

C