Apply a Flat, Inner Bevel.

NOTE: This may take some time on slower computers. Either take an eye break while this is happening or you can skip the bevel if you want.

If you do successfully create the bevel, convert the bevel to bitmap (Arrange > Create Bitmap Copy) using the True Color + Alpha Color Depth: setting.

Resize the bitmap and center it over the deep red background we created earlier.

Clone the deep red background rectangle and change the fill to a brooding black and deep red Fractal Cloud fill.

Apply a Flat, Stained Glass transparency and change the Transparency slider amount to 10%.

This creates a very subtle, dark and ominous background image.