Unable to scroll the expandable menu on the left of docs

[jkonicki]

Report:
When left menu is expanded it doesn't allow scrolling the menu itself. At high dpi scaling (cntrl+plussign key) the bottom of menu falls off and doesn't allow any way of being scrolled without scrolling the whole page, limiting its usefulness as navigation.

[cf-gitbot]

We have created an issue in Pivotal Tracker to manage this:

https://www.pivotaltracker.com/story/show/164992912

The labels on this github issue will be updated when the story is started.