CSS media query

One of the ways to keep layout separated from the content is by using CSS files. However, the need may arise to provide different CSS styles for different devices. This is where the media query comes into play. By using statements like:
@media screen and (min-width: 400px) and (max-width: 700px) { … }
the CSS definition between brackets will be used if the width of the area in which the page is rendered is between 400 and 700 pixels and the media (device) is a computer screen.
Please refer to the W3 site for more examples and how to use this convient way of dynamic selection of stylesheets.
http://www.w3.org/TR/css3-mediaqueries/