Make it easier to override tab-size

[nuxodin]

change :root to html because :root has a higher specificity than html

[sindresorhus]

What's the benefit of lower specificity? I don't see how anyone would care to override this.

[nuxodin]

If you want to override tab-size for a specific element, for example a custom element, :root wins.

:root {
	tab-size: 4;
}
custom-pre { /* does not overwrite */
	tab-size: 3;
}

I don't see any reason to use :root.

And you save one byte :)

[sindresorhus]

From the original issue (#17):

Using :root so users can easily override it on a per-element basis.

Either I was confused back then or we're missing something now.

[nuxodin]

My wisdom comes from here:
https://css-tricks.com/a-complete-guide-to-custom-properties/#the-root-thing

And it makes sense, :root is a pseudo class and has 0.1.0 specificity where html has 0.0.1