Float not working

Hey there,
I set the TOC to float on the left, and set it up as a widget on the left sidebar. When viewed on PC, the TOC appears on the left, but fails to float when scrolling down. It remains stuck at the top of the page. The same issue is seen on mobile, although this time the TOC is stuck at the bottom on the page.

I am using Customizr theme and already have the top bar that floats on the top, and a small “return to top” arrow that floats on the right, these floats have been setup by the theme itself. I am using Chrome.

Is there something I am doing wrong? I cannot seem to get it to float

The page I need help with: [log in to see the link]