Nah, I can't seem to do it on my own. I thought I might be able to do it, but I can't.
Here's a side by side comparison between the modal's appearance with a gradient, and without a gradient. The gradient one is on the left. The border one is on the right.
I closely cropped the images but I did absolutely no editing on the modal positions displayed here. The gradient one is slightly off, and I can't seem to get it positioned exactly the same as the border one.