:root CSS pseudo-classThe :root CSS pseudo-class matches the root element of a tree representing the document. In HTML, :root represents the <html> element and is identical to the selector html, except that its specificity (0-1-0) is higher than html's (0-0-1).
/* Selects the root element of the document:
<html> in the case of HTML */
:root {
background: yellow;
}:root {
/* ... */
}:root can be useful for declaring global CSS variables:
:root {
--main-color: hotpink;
--pane-padding: 5px 42px;
}