make multitasking-view shadows mimic theme shadows

[Danielle Foré]

At the moment when you go into multitasking view, shadows get larger, darker, and change position.

This means the light source moved and got way brighter while the windows also moved farther away from the background.

Maybe it makes sense for the shadow to get bigger (windows moving farther on the z axis from the background), but that would imply that the shadow should become lighter, not darker.

Also I don't think it makes sense for the shadow to become centered (meaning the light source changed position).

We should more closely mimic the shadows from the theme to avoid odd changes in lighting.