* I don't think the words "Back to" are necessary. On other back buttons we just put the thing you're going back to. So "Library" and "Welcome Screen" are probably fine.
* The window title doesn't seem to update when you change screens. It should show "Videos" on the Library and Welcome pages
* I think these pages should be added to a Gtk.Stack so we can have a nice swipe animation when moving back like you see in Switchboard
* There should probably be some kind of placeholder for when Videos is unable to fetch a poster image
* The shortcut "alt + left" should activate the back button
* I don't think the words "Back to" are necessary. On other back buttons we just put the thing you're going back to. So "Library" and "Welcome Screen" are probably fine.
* The window title doesn't seem to update when you change screens. It should show "Videos" on the Library and Welcome pages
* I think these pages should be added to a Gtk.Stack so we can have a nice swipe animation when moving back like you see in Switchboard
* There should probably be some kind of placeholder for when Videos is unable to fetch a poster image
* The shortcut "alt + left" should activate the back button