I was thinking more of just a button on a normal screen thats fixed to the bottom and centered. That way when they scroll down the button remains visible at all times.
.fixed is used to set it to the bottom of a non-scrolling screen.
.sticky is used to set it to the bottom of a scrolling screen.
.blur is used to blur the background of the sticky button, so the content is slightly visible.
I found that creating a separate container that only housed the button and apply the CSS to the container, not the button gave me the best results.