CSS Responsive Design
Mobile first design
Mobile first design is a design strategy where we first design a web page for small screen devices before we add media queries that enable more features for larger devices.
This strategy can be categorized as a progressive enhancement strategy where we build the core foundation of the page before we add bells and whistles.
The hardest design choices are often all related to limited screen real estate, so once we figure out how a web site should look on small devices, the design for larger devices will mostly fall into place by their own accord.