style background when sticky not working

Hi,
Please post the site URL so we can have a look. In theory, what you posted is fine.

If you have a minute, please leave a review. It’s what keeps support going. Thank you! https://www.ads-software.com/support/plugin/sticky-menu-or-anything-on-scroll/reviews/#new-post

lobeltree.com /astra/

I have put this in Extra CSS just to test:

.element-is-not-sticky {
background: none;
}
.element-is-sticky {
background: black;
}

Idealy I want the backround initially transparent and when moving down the page, have a semi transparent black background. Tried this as well, but no success. background-color: rgba(0,0,0,0.39);