It's a mobile phone world.And a tablet world. And a laptop world. The fact is, it's a multi-screen world and your web sites and applications have to live in it. Perhaps, you're looking for an easy way to implement the principals of responsive design in your own work. Perhaps, you want an easy mobile-first framework to wrap around your own work. Or, maybe, you just want to learn the right way to do things in a multi-screen world.From the screen in your users' pockets to the giant 4K desktop screen, your apps and web sites have to look good everywhere-- but how does someone create for such varied screen sizes and resolutions-- The answer is Bootstrap.Bootstrap is a visual, client-side framework that lets you build gorgeous mobile apps and build those into full screen-compliant applications.