Hi,
Yes, it’s possible, but every theme requires a different way to achieve it.
I paste here one CSS that makes the background darker. Of course, it will not work in your case, but you or your Web Developer will be able to understand how it should work.
body.dgwt-wcas-open > #wrapper > #main:after,
body.dgwt-wcas-open > #wrapper > #footer:after,
body.dgwt-wcas-open > #wrapper #top-bar:after,
body.dgwt-wcas-open > #wrapper #wide-nav:after {
content: '';
display: block;
position: absolute;
left: 0;
top: 0;
bottom: 0;
right: 0;
margin: auto;
width: 100%;
z-index: 1;
background: rgba(0,0,0,0.6);
}
As you see, you have to cover all elements excluding the search bar and its parent’s elements.
Best
Damian