The basics on Responsive Web Design/Development from Google Developers. With mobile devices becoming a fast growing way to view the web, most website are not optimized to meet the layout of a mobile device. There is a multitude of different screen sizes across phones, “phablets”, tablets, desktops, game consoles, TVs, even wearables. Screen sizes will always be changing, so it’s important that your site can adapt to any screen size, today or in the future.