Almost there!
I managed to get the appearance I was looking for:
I added a style attribute in the GroupRowRender event to change the background color, and called my custom class to change the text appearance.
args.Attributes.Add("style", $"background-color: #479CC8");
args.Attributes.Add("class", $"{(true ? "frameworkDomain" : "frameworkDomain")}");
Modified style class for text
Is there a way to incorporate both of these requirements in the class alone?