I want to insert a grey vertical divider that splits the two sides evenly to show a logical division. Since the content on the two sides can vary in height depending on what the user selects, the divider needs to scale appropriately -- in other words, can't be fixed height.
As an aside, ideally this style element would be something that I could conditionally insert and remove. Obviously some sort of div would give maximize control.
Here's my existing HTML/CSS code: