How to make absolute button CSUI

Hey, a newbie here trying to create a button that appears on certain pages, always on the bottom right of the screen (this location never changes.) I know plasmo has a neat CSUI system that can render react components through just exporting them through .tsx files in a contents directory. However, this code doesn't seem to work, and when I try and anchor it to any other element (h1, as shown in picture) it is no longer absolute to the bottom right of the screen, and it scrolls along with the page. Is there something I'm doing wrong? I tried just appending a vanilla button in my content.js file and it worked perfectly, as shown in the photo. But given that I'm using ant design and plasmo, I'd like to be able to render react elements in the clean plasmo CSUI way. Any help would be greatly appreciated!