I use Gradient's in some of my usergroups:
Add to custom CSS
.Gradient{
background-image: -webkit-gradient( linear, left top, right top, color-stop(0, #673AB7), color-stop(1, #ad00ff) );
color: transparent;
-webkit-background-clip: text;
background-clip: text;
font-weight: bold;
font-style: italic;
}
Change the 2 Hex Color codes to your desired Colors.
Next go to the usergroup that will have the Gradient and go to group formatting
add this:
<span class="Gradient";> </span>
And Done.