Add a Spacer Element

There are cases in which some negative space needs to be added. For example, I have a highlight box all the way to the left of a page with a few options along the top. The content in the middle (not in the highlight box runs down pass it. I would like to have the highlight box run down as far as the content does, but it stops where ever its last element is. So my idea is to add an element for adjusting the negative space. Now, I am aware that I can create a custom sidebar, but I think it can only be viewed on the right side of a page, and I would like it to star after a body of text and pinned right on top of the page. Does this sound like a possible addition?