Not getting completely dark on mobile

Hello,

I love the plugin! it is fantastic!

I have one issue. Although it seems to be working perfectly on desktop, on mobile the homepage is not getting dark fully (it works on the header and footer, but in the middle part where the posts are, it does not).

Let me show you what I mean:

This is desktop (works fine): https://ibb.co/kStsT0s

This is mobile: https://ibb.co/rkXqr3K

Also is your plugin very intensive? I mean I hope it is lightweight and does NOT put a lot of load on the server (I use shared hosting so I have limited resources).

Please help! I really want to use the plugin!

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