This document discusses responsive web design (RWD). RWD makes web pages render well across devices and screen sizes by using fluid grids, flexible images, and CSS3 media queries. It allows the page to apply different style rules based on the device's characteristics, like browser width. RWD has become important as over half of internet traffic now comes from mobile devices. Google announced in 2015 that it would boost rankings for mobile-friendly sites viewed on mobile.