"Fixes" the collapsed navigation state

What does this MR do and why?

This fixes the collapsed state toggle button to the top of the viewport instead of the top of the page. Previously, if you collapsed the navigation, you would have to scroll to the top of the page to open it back up. This fixes it to the viewport so it stays with you as you scroll down the page.

See the attached video for more context.

Screenshots or screen recordings

collapse_fixed.mov

How to set up and validate locally

1. Enable the feature flag:

echo "Feature.enable(:super_sidebar_nav)" | rails c

1. Enable the user setting from the user dropdown:

1. The super sidebar should now appear on every page.
2. Hit the collapse Icon in the sidebar to close the sidebar

1. Scroll down the page and watch it follow you.

MR acceptance checklist

This checklist encourages us to confirm any changes have been analyzed to reduce risks in quality, performance, reliability, security, and maintainability.

• I have evaluated the MR acceptance checklist for this MR.