::before

Last updated on: September 12, 2012

::before is a pseudo element which allows you to insert content onto a page without it needing to be in the HTML. While the end result is not actually in the DOM, it appears on the page as if it is, and would essentially be like this:

div::before {
  content: "hi";
}

<div>
  -- Rest of stuff in side div --
  hi
</div>

The value for content can be:

• A string: content: "a string"; - special characters need to be specially encoded as a unicode entity. See the glyphs page.
• An image: content: url(/path/to/image.jpg); - The image is inserted at it's exact dimensions and cannot be resized. Since things like gradients are actually images, a pseudo element can be a gradient.
• Nothing: content: ""; - Useful for clearfix and inserting images as background-images (set width and height, and can even resize with background-size).
• A counter: content: counter(li); - Really useful for styling lists until :marker comes along.

Note that you cannot insert HTML (at least, that will be rendered as HTML). content: "<h1>nope</h1>";

Every browser that supports the double colon (::) CSS3 syntax also supports just the (:) syntax, but IE 8 only supports the single-colon, so for now, it's recommended to just use the single-colon for best browser support.

More Information

• A whole bunch of cool stuff they can do.
• Support chart on transitioning/animating
• Screencast Introduction
• Using with sprites

Browser Support

Little issues:

• Firefox 3.5- wouldn't allow absolute positioning of pseudo elements.
• In Opera 9.2, whitespace is always displayed within this pseudo-element as if it’s pre text.
• IE 8 doesn't support z-index on them