如何调整100％高度以包括添加元素的高度

I have a div that is added dynamically using JS that includes an overlay and a contained element that should scroll with the page as necessary (I don't want any scrolling to happen within that div, which resizes to fit the content). The overlay is set to width=100% and height=100% to cover the entire page. However, when the contained div ends up being taller than the viewport, this causes the overlay to stop short after the height of the viewport.I have a div that is added dynamically using JS