Build overlapping 3D widget panel(with depth like z axis) for HUD and animation

Hi, i have a very strange problem. when i use additive in blend mode of material, my display do not have a black background in overlap part but i can not see it in BP_actor viewport. if i change it to transparent or masked, i can see it in actor viewport but I got a black background like before. Dont know how to solve this strange problem.