supply default font-size with <h1> override
set font preference to Arial

If Open Sans is available on the source site, use it for the footer.
provide default styling for text-input elements

In addition to the default styling, we need to increase the specificity
of the Copy Link input element. This is because the attribute and class
selectors have equal specificity.
displace the body to make room for the drawer

The body needs to be displaced in the event that there are elements
added to the page that have a z-index applied. Otherwise, those elements
may appear to cover the drawer.
animate the drawer opening/closing
set a flag for whether the drawer should animate
register cleanup function

The ad hoc changes made to the DOM need to be cleaned up if Betterlink
is removed from the page.