Hello I have a similar question. On my page ( https://www.thegirlwhocanbemoved.com/travel-aid ) I have the code:
Background Image:
body#collection-60c2c0bbe7029058c001fb90 .main-content {
background-image: url(https://static1.squarespace.com/static/60bdc87395311344b2c32700/t/60c2f21d25578e34f1291620/1623388705704/jeremy-zero-EzvUzveWprI-unsplash.jpg);
background-repeat: no-repeat;
background-size: cover;
background-position: center center;
opacity: 1
}
I am trying to add this as an overlay to the entire page:
body#collection-60c2c0bbe7029058c001fb90 .main-content {
background: RGBA(3, 127, 138, .8)!important;
}