Theme is not mobile responsive

The theme is not responsive to mobile devices. I’ve searched in the forum and tried adding the following to additional_css:

@media only screen and (min-device-width: 320px) and (max-device-width: 480px){
body {
   padding: 0;
   margin: auto !important;
   width: auto !important;
}
}

@media (max-width: 768px){
.wp-block-cover.aligncenter.has-background-dim-10.has-background-dim.has-parallax.has-background-gradient {
    background-size: contain !important;
    background-repeat: no-repeat !important;
}
}

but it’s still not working for me. The homepage had image and text overflow on mobile, and my single posts are also having the same issue with gallery slider. Any help is appreciated!!

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