I pulled this down for Unity 2022.X which STILL doesn't support putting in extensions. I found that it worked better if I updated the offsets around line 76 to be:
rect.x += (32f + GUI.skin.label.CalcSize(content).x);
rect.y += 0f;
And changed the color at line 24 to be
color = new Color(.8f,.8f,.8f);