Add hover state to window controls

[wpkelso]

Problem

Window controls are not responsive to the user's cursor on desktop, and don't explicitly show they can be interacted with. This could cause confusion for some, and generally doesn't follow standard practices.

Proposal

Add hover state highlight to window controls to better communicate that a user is able to interact with the said control.

Prior Art (Optional)

No response

[wpkelso]

Potentially affected and/or blocked by #1278