CSS Transitions with pseudo elements

Webkit browsers don't apply transitions to pseudo elements such as :before and :after

HTML

<div id="elem">Hello World</div>

CSS

div#elem
{
    background: red;
    border: 1px solid green;
}

div#elem:before
{
    content: 'before the hello';
    background: yellow;
}

div#elem:after
{
    content: 'after the hello';
    background: green;
}