WebGL and Canvas Scaling - Canvas won't scale according to Browser Window Size

Hello, I have this pretty annoying issue where the WebGL build of my game won't scale according to the Browser page. Is there an easy solution for that, any Asset Store assets that can help or any support on the paid version of Unity?

Also in Fullscreen mode the background is black while when I enter the normal Browser Window mode it becomes white. Any ideas for that as well?