What's wrong? Describe the what you're seeing

On some documentation pages (such as https://segment.com/docs/connections/sources/catalog/libraries/website/javascript/) the user is unable to see the full list of heading tags within the On This Page box to the right without scrolling to the entire end of the page. Example shown in screenshot:

Problem location

Issue is within documentation pages with any significant amount of On this page header tags, such as https://segment.com/docs/connections/sources/catalog/libraries/website/javascript/

Suggestions for a fix

The suggested fix would be to give the On this page box it's own, separate scrolling.