Collapsible side navigation **Proposal**

[Mattchewone]

I've often found when navigating the docs and I am looking at a page where there are lots of children / siblings on the side navigation that it can become unwieldily at times and there is not currently a way to collapse either the children or the top level item.

As I have selected can-symbols within Polyfills I can no longer collapse the top-level Polyfills menu item, we could allow it to be collapsed and have it be highlighted to show this menu is where our current page navigation belongs.

I'd also like to be able to select Polyfills / Typed Data to open / close rather than just the +, as I've often clicked the title to expand.