How do i add 2d background to the 3d model in mainmenu?

hi , how do i add 2d background to the 3d model in mainmenu? i want to know the right way which can make me add 2d background to the 3d model in mainmenu,but if i ues widget component ,the widget component’s color is different from the original image ,How to make the same color and adapt to different mobile phones?

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