Right, a gradient overlay is probably the best approach… you can define two backgrounds at once like this:
body {
background: radial-gradient(circle at center, rgba(255,255,255,1) 35%, rgba(255,255,255,0)) fixed, url(https://forums.pickleballist.com/uploads/default/original/1X/b7df60bb8a3fd1584f393dee365865ca83e4906e.svg) center top / 300px auto ;
background-attachment: fixed;
}
Or if you only want this background gradient on topic pages and not other pages (like profiles, topic lists, etc)… you could put the pattern on body, and then the gradient background on top of that in .archetype-regular #main-outlet { }