Not sure what Googlebook is, but in general: I want to be able to move my pointer to the top right corner and click to close the window.

And before you make some claim like "use keyboard", the UI includes these window elements for a reason. Top bar makes them less friendly to use: They're tiny and with top bar it's an aiming game instead of a quick way to do something with a mouse or a touchpad.

As an i3/sway user I don't greatly care about this because I already have things the way I like, but I understand the frustration of the OP.