How to make "diamond" gradient?

[smbv1]

Hello, I would like to make a gradient some kind of a Diamon Gradient, but rotated to 45 degrees, which is going to look as a regular 4 corners dark gradients, here is a reference:

I’ve tried to use DiamondGradient function, but could not find the way to rotate it to 45 degrees. Please help

[smbv1]

This is what I was able to do, so cool!
Now I would like to make the edges to look sharper, less smooth.