Markdown controls

[bidi47]

linked to dotkernel/documentation-theme#11
this PR has the js, css to keep the documentation-theme PR clean

[alexmerlin]

Suggested change

	.then(function (markdown) {
	return navigator.clipboard.writeText(markdown);
	})
	.then(async function (markdown) {
	return await navigator.clipboard.writeText(markdown);
	})

If you don't wait, then if writeText fails (very unlikely, but possible), the user would see a transition like this:
"Copy Page" -> "Copied" -> "Copy failed" -> "Copy Page"
With an async flow, the messages would show up correctly.

The above is not tested - please test it first!