sidebar should start scrolling before

This error happens on the support portal and the Tor Browser User Manual.

Steps to reproduce:

• Open https://support.torproject.org/ in a small screen, or with high zoom.
• scroll down until you access the bottom items of the sidebar (i.e. Get in Touch)

Error: you need to reach the bottom of the whole page until the sidebar scrolls.

What should happen instead: the sidebar should start moving earlier, so you can access the last items without having to scroll to the bottom of the page.