Full screen on Mac (Photoshop Elements 2019)

I am using my (recently bought in-store) Photoshop Elements software to illustrate and create backgrounds. I need to make the window (not just the page I'm working on, the whole Photoshop window) fullscreen so I can easily switch between references and other things I'm using to work. The green "full screen" button at the top of the window only extends it, it doesn't make it full screen. I've combed through all of the settings and I can't find anything that helps. Is there a way to do this? Please help!