Do you have a quick sample available? I am not using this, nobody else answered I would look at your example and check the resulting markup and tell you if there is any indicator for the currently active item.
But I am afraid there won’t be any, because it’s AFTER the page loaded that you click the TOC item and end up on the corresponding item on the page.
I would expect something like #TableOfContents > ul > li > a:active to work, but no guarantee.
Did you try #TableOfContents > ul > li > a:active? The link should be active if it’s clicked. This might not work with directly loading the page though…