Add a fill or effect to a shape or text box - Microsoft Support
https://support.microsoft.com/en-us/office/add-a-fill-or-effect-to-a-shape-or-text-box-28d8dc7f-5bc2-4f83-bb07-615f84ca77d1
To add a fill or effect, click your shape, click Format, click the arrow next to Shape Fill or Shape Effects, and select a color, gradient, texture, or effect. Click the shape that you want to fill. To add the same fill to multiple shapes, click the first shape, and then press and hold Ctrl while you click the other shapes.