How to set box to move dynamically with page

I have my pages set up so that there is a default boarder for every page. However, there is no shadow option for the current setting so I decided that a good workaround would be to create a box with a shadow effect and attach it to the top, bottom, and sides of the pages. It works wonderfully for pages that don’t change size vertically, but on pages where text boxes lengthen the page vertically I get the following problem:

I want the box to be attached to the bottom of the page so when the page changes height, the box does as well. Is there any way to do this?

Boxes can’t change size, However you may adjust height be creating multiple boxes withn that collapse or expand accordingly to your window height that you may call from wix.window.