[css] CSS Equivalent of the "if" statement

There is no native IF/ELSE for CSS available. CSS preprocessors like SASS (and Compass) can help, but if you’re looking for more feature-specific if/else conditions you should give Modernizr a try. It does feature-detection and then adds classes to the HTML element to indicate which CSS3 & HTML5 features the browser supports and doesn’t support. You can then write very if/else-like CSS right in your CSS without any preprocessing, like this:

.geolocation #someElem {
   /* only apply this if the browser supports Geolocation */
}
.no-geolocation #someElem {
   /* only apply this if the browser DOES NOT support Geolocation */
}

Keep in mind that you should always progressively enhance, so rather than the above example (which illustrates the point better), you should write something more like this:

#someElem {
   /* default styles, suitable for both Geolocation support and lack thereof */
}
.geolocation #someElem {
   /* only properties as needed to overwrite the default styling  */
}

Note that Modernizr does rely on JavaScript, so if JS is disabled you wouldn’t get anything. Hence the progressive enhancement approach of #someElem first, as a no-js foundation.