While I dont see on any screen that the login field is getting shown correctly, yes the cancel button looks fine and the fields may look fine, stuff around it is messed up.
Try booting in safe mode like suggested but I still say your graphics failed on you. Even if the graphics are failing, that doesnt mean nothing can be correctly displayed. There can be parts which are fine and parts which are not.
I blurred out my info so that part is working fine, albeit extremely slow... As in 5 minutes or more just to log in. I only see the graphics issues upon login although I nwcer watch videos or do any photo work anymore due to the slowness of my computer; it's impossible and a waste of complete time. Thank you for your feedback!!!