:rootThe :root pseudo-class matches the root element of the document, usually the <html> element.selectorsSelectorswidely2015-07-292018-01-29https://drafts.csswg.org/selectors-4/#the-root-pseudohttps://developer.mozilla.org/docs/Web/CSS/Reference/Selectors/:rootcss.selectors.roothttps://nowyoucanuse.com/features--root.html