Is it possible to add a background image for the column with Custom CSS?  I’ve set an image for the header but I want to replace the solid color BG2 with an image and can’t...

Also any suggestion for mobile background scaling on my store page for Eves Drop would be appreciated!

There's nothing we've done that would be stopping you from doing this. Make sure you've used the correct CSS syntax, provided a valid image URL, and that the precedence of the selector you're using beats out the precedence of the default CSS. I recommend opening your browser console's CSS inspector to see what's going on.