Web Design with HTML5 and CSS3 is your step-by-step guide to learning how to embrace responsive design for all devices. You will learn how to develop your existing HTML, CSS, and JavaScript skills to make your sites work for the modern world. Web sites and apps are now accessed on a wide range of devices with varied sizes and dimensions, so ensuring your users have the best experience now mean thinking responsive.

Responsive Web Design is the notion that modern websites should adapt to, and display optimally on any, indeed all, screen sizes. This is accomplished by fluid layouts using formulaic (a specific formula) percentages for CSS measurement instead of pixels, and using CSS media queries to target different screen sizes.

There are generally two principal ways for developing websites to specifically target multiple devices: develop separate websites for mobile and desktop, or develop responsive websites that adapt to all screen sizes. We will only discuss the latter, since the former is a costlier alternative that has some specific use cases depending on the target audience and the purpose of the website.