Feature request: Swipe on backdrop to close sidebar

[sawanm9000]

The sidebar can already be closed by clicking/tapping the backdrop right now but it's not very intuitive especially on mobile. Until swipe to pull/push is implemented (#1), this would be a good alternative. (See how it's done on Google search on mobile). "onmousedown" instead of "onClick" and "touchstart/ontouchstart" or "touchmove/ontouchmove".

Also: fade out the backdrop on close before disappearing - it's hard to animate when it just cease to exist in the DOM.