Duplicate an element and put it behind that element, then offset it and overlay it with a dark repeating pattern, creating a shadow effect.
If you want to add some branding to a bold drop shadow, and also create a retro look, this can be a good way to do it.
This is quite bold, so it needs to make sense with your brand.
Simple patterns and dark colours will work best. If it's too bright or too flashy, you might find that the shadow distracts the user from the element casting it, which doesn't help them understand where they should be focusing.