Just copy & paste this into the "user name CSS" of the group where you wanna add this cool effect
background-image: linear-gradient(270deg, #d83b3b, #e3ed20, #20ed2d, #2082ed, #cd20ed, #20edbe) !important;
background-size: 1200% 1200% !important;
-webkit-animation: TestBanner 30s ease infinite...