[Land and See - Side bar] Side bar is too short when user is in another app accessing web page

**Current**
User is in email > clicks link to Land and See > user clicks menu icon and the side bar opens, showing the page underneath the bottom.


**Should be**
Side bar adapts to length of viewport, no matter what app its in. cc @camelburrito @ericlindley-g is this a technical limitation?

Reproduce the email-to-Land-and-See flow, open the menu icon, and inspect the sidebar implementation used by that page. Compare its height with the viewport while the page is opened from another app. Done means the sidebar adapts to the full viewport and no longer reveals the page beneath the bottom edge.

Written by the indexing model from the issue text.