What's the difference between CSS3's :root pseudo class and html?

问题

I can't seem to find much information about this.

Smashing Magazine seems to be saying that html and :root are the same thing but surely there must be a tiny difference?

回答1:

From the W3C wiki:

The :root pseudo-class represents an element that is the root of the document. In HTML, this is always the HTML element.

CSS is a general purpose styling language. It can be used with other document types, not only with HTML, it can be used with SVG for example.

From the specification (emphasis mine):

This specification defines Cascading Style Sheets, level 2 revision 1 (CSS 2.1). CSS 2.1 is a style sheet language that allows authors and users to attach style (e.g., fonts and spacing) to structured documents (e.g., HTML documents and XML applications).

回答2:

One technical difference between them is that :root - being a pseudo class has a greater specificity than html (a type selector)

:root {
  color: red
}
html {
  color: green;
}

<div>hello world</div>

So, in the above example, the :root selector overrides the html selector and the text appears red.

回答3:

For HTML documents, there is no difference - your root element is the <html> tag, so html{} and :root{} are (besides from a difference in specificity) semantically equivalent.

However, you can apply CSS not only to HTML, but all XML-like documents. That's why :root is there - to target the document's root element regardless of document type. Most people are confused by the difference because the overwhelmingly predominant use case for CSS is styling HTML documents.

Example: You can style SVG documents with CSS. When styling it, your root element will (obviously;-)) not be html but svg. See the following list of SVG tags.

来源：https://stackoverflow.com/questions/15899615/whats-the-difference-between-css3s-root-pseudo-class-and-html

标签

css

css3

css-selectors

pseudo-class