Additional Dropdown functionality

[emplums]

The Dropdown component should also close on outside click. It might be worth looking into whether or not we could use https://github.com/github/details-menu-element inside of our component and what the implications might be! Would be a good trial for using the web system's team's web components inside of our components.

[shawnbot]

The low-tech way to do this might be to style the <summary> in the same way that details-overlay and details-overlay-dark do, which makes the summary hit area sit above everything "below" the content so that tapping it toggles the <details> element natively.

[emplums]

Oh good idea! This probably makes most sense to implement on Details, unless there's any reason why someone wouldn't want a Details element to close on outside click? We could put both functionalities in though and control it by a prop