Problem with button alignment

That CSS is for post loops.

Are you trying to make the images with extra-margin-bottom go full width on mobile?

If so, try this CSS:

@media(max-width:768px){
    .wp-block-image.extra-margin-bottom figure{
        float: none;
        width: 100%;
    }
    .wp-block-image.extra-margin-bottom figure img{
        width: 100%;
        height: auto;
    }
}

Note: This won't go full-width of the viewport. It will only go full-width of its container like this: https://share.getcloudapp.com/ApuYN4xo

PERFECT! Exactly what I was looking for, Elvin. Thanks!!

No problem. Glad to be of any help. :D