Looking at the site, you have a black 50% transparent background on maybe one of the layers?
Are you looking to replace that or just “Frost” it or “Blur” it?
The reason I ask is the frosted backgrounds both CSS and images are usually white?
If you want to just “blur” what you have try adding this CSS
.layerzLayer {
backdrop-filter: blur(5px);
}
I’d probably reduce the opacity you have now on the black to around 20%.
I did it to your site and it would look like this: