Media queries are a CSS language feature that allows an author to conditionally apply CSS rules according to characteristics of the device or window in which an application is being viewed. Responsive design can be accomplished through a combination of techniques including conditionally applying CSS rules with media queries and choosing layouts which are flexible according to the content they hold. Mobile-first design is a principle that should be employed when designing and building responsive web applications. By default, mobile browsers will assume that a website has not been designed to accommodate the narrower viewport of such a device.
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