Door panel help, PLEASE!

[WillAdams (William Adams (Carbide 3D))]

Uh, we covered this:

I'm trying to make a panel for my front door

I’ve looked for a grayscale 3d of a pyramid shaped like the bottom panel of the door but can’t find anything close. Every one I find is perfectly square. Regrettably I don’t know how to create the image. But it will measure 26 7/8” x 19 7/8” as a finished product. If anyone can help out it’d be greatly appreciated. [Screenshot_20210706-122650]