:root selector allows you to target the highest-level "parent" element in the DOM, or document tree. It is defined in the CSS Selectors Level 3 spec as a “structural pseudo-class”, meaning it is used to style content based on its relationship with parent and sibling content.
In the overwhelming majority of cases you're likely to encounter,
:root refers to the
<html> element in a webpage. In an HTML document the
html element will always be the highest-level parent, so the behaviour of
:root is predictable. However, since CSS is a styling language that can be used with other document formats, such as SVG and XML, the
:root pseudo-class can refer to different elements in those cases. Regardless of the markup language,
:root will always select the document's top-most element in the document tree.
In the example below, the
:root pseudo-class selector is used to create a background color behind the
<body> element. In this case, the same effect could be achieved by using the
html element selector in our CSS instead.
Points of Interest
- While the
htmlselector both target the same HTML elements, it may be useful to know that
:rootactually has a higher specificity. Pseudo-class selectors (but not pseudo-elements) have a specificity equal to that of a class, which is higher than a basic element selector.