Modal jumps position when the viewport is resized
Created by: valerie-makes
Demo: https://jsfiddle.net/techdavid/g89ts0rs/2/
When the viewport is adjusted, the modal gets a margin applied to it, making it jump position slightly to the left (once only).
For the problem to occur, the main page content needs to overflow but not the modal. _adjustDialog()
should be called when the modal opens initially so that this doesn't occur.