Responsive Web Design is an approach of laying-out and coding a website such that the website provides an optimal viewing experience - ease of reading and navigation with a minimum of resizing, panning, and scrolling - across a wide range of devices (from desktop computer monitors to mobile phones). Smartphone and tablet adoption rapidly increases, so does the importance of mobile-friendly websites. Smartphones and tablets have changed the approach toward design and user experience. Before the spread of mobile devices with advanced web-browsing capability, web designers had only one primary challenge to deal with keeping the same look and feel of their websites. Responsive web design sites are fluid, meaning the content moves freely across all screen resolutions and all devices. Both the grids and the images are fluid. Just as a liquid spreads out or draws in to allow its content to fill an allotted space and retain its appearance, responsive web design's fluidity achieves the same result with website content on a device screen.