As you're, no doubt, aware that CSS stands for Cascading Style Sheet. By their very nature styles further down a cascading stylesheet override equivalent styles higher up (unless styles higher up are more specific). We can therefore set base styles at the beginning of a stylesheet, applicable to all versions of our design, and then override relevant sections with media queries further on in the document. For example, set navigation links as simple text links for the large viewport version of a design (where it's more likely that users will be using a mouse) and then overwrite those styles with a media query to give us a larger target area (for finger presses) for more limited viewports.