Hey Kathryn,

The only thing I'd make sure of is that the sticky button either occupies an empty spot in the topnav bar, or at least doesn't obscure the links in the topnav.

Have you considered having the escape button live at the bottom-right hand corner of the screen, similar to a "jump to top of page" button on longer news articles? For example, this website has a green button at the bottom-right of the page that appears when you scroll down and acts as a quick "jump top top" button. That would make sure that you're not covering topnav items with the escape button.