[BUG][UI]Escape key should close most screens
from 
Elemental Forums
Elemental Forums
It makes it easier to play when using mostly the keyboard. The <esc> key is a lot simpler to hit than finding the done/cancel button using a mouse.
City Detail screen doesn't respect this.
The funniest one I've seen so far is if you go into options/save game and hit <esc> the options screen closes, but the save screen doesn't, even though it has the keyboard focus.