Adjust TOC scrollbar
Adjust TOC scrollbar

This built upon previous code so that when the scrollbar is viable the bottom arrow is not covered by the "Next" navigation button.  This is actually an improvement over ReadTheDocs as the same overlapping behavior happens there.

waylan/mkdocs,mkdocs/mkdocs,waylan/mkdocs,mkdocs/mkdocs,lukfor/mkdocs,lukfor/mkdocs,lukfor/mkdocs,jimporter/mkdocs,waylan/mkdocs,jimporter/mkdocs,mkdocs/mkdocs,jimporter/mkdocs