Floating overlay for screen share

Today I found that I can't hide or close a something like floating subwindow for current screen share. 

Why did you do it? It's a stupid way. I can't move it whatever I want. I can't close it. 

Why should I see this window over my chats?

Loot at the screenshot, I marked it by red frame:

WHY??? Tell me, why are you acting like a ms with skype?