Mobile First
Mobile first, a form of progressive enhancement, is a web-development and web-design approach that focuses on prioritizing design and development for mobile screen sizes over design and development for desktop screen sizes. The rationale behind the mobile-first approach is to provide users with good user experiences at all screen sizes—by starting with creating a user experience that works well on small screens, and then building on top of that to further enrich the user experience as the screen size increases. The mobile-first approach contrasts with the older approach of designing for desktop screen sizes first, and then only later adding some support for small screen sizes.