If you want to edit the default Mendix login page, you will need to edit the HTML file directly. I dont know if you can get that from Mendix Studio. However, it is not advised to do this.
The best way to go would be to create your own custom login page, which you then can style any way you like.
Yes this is true, it got changed in recent updates, I don’t remember exact version, but it was changed post 8.XX.
In recent versions, you have yo edit using studio pro