Surfing the Internet on mobile devices has overtaken doing so on actual computers — a while ago, in fact.
It’s crazy to think about, but that’s really how it goes in 2019 with smartphones and tablets being as ubiquitous and awesome as they are. That said, the concept of mobile-first web design has a lot of traction. Are you wondering what the difference is between that and responsive design? Well, they do the same thing but start from opposite places: