Without the CSS3 media query module, we would be unable to target particular CSS styles at particular device capabilities, such as the viewport width. If you head over to the W3C specification of the CSS3 media query module (http://www.w3.org/TR/css3-mediaqueries/), you'll see that this is their official introduction to what media queries are all about:
HTML 4 and CSS2 currently support media-dependent style sheets tailored for different media types. For example, a document may use sans-serif fonts when displayed on a screen and serif fonts when printed. 'screen' and 'print' are two media types that have been defined. Media queries extend the functionality of media types by allowing more precise labeling of style sheets.
A media query consists of a media type and zero or more expressions that check for the conditions of particular media features. Among the media features that can be used in media queries are 'width', 'height', and 'color'. By using...