via Webmonkey:

Variables in cascading stylesheets are now available in the nightly WebKit build.

CSS without variables:
//Sets the background of the page and tables to the hex code for the color grey
body {
   background-color: #eceae1;
}
table {
   background-color: #eceae1;
}

With CSS variables:
//Defines "DefaultBGColor" to light gray
@variables {
   DefaultBGColor: #eceae1;
}
//Sets the background and any table on the page to the default background color
body {
   background-color: var(DefaultBGColor);
}
table {
   background-color: var(DefaultBGColor);
}

Jeffrey Barke is senior developer and information architect at theMechanism, a multimedia firm with offices in New York, London and Durban, South Africa.