There’s a misconception that mobile first means building the mobile app (iOS/Android) first. Mobile first is about prioritizing the mobile web experience for your product or service. Let me explain…
Your beautifully styled web application is responsive so the design flows well from desktop sized browsers down to mobile sized browsers. To make your app look great on a mobile screen, you simplify the look by removing unnecessary elements. There’s less structure, less styling, less of everything to provide your users with a great mobile experience.
Since your phone is generally on a slower connection and performing with less power, front-end developers use a mobile first approach to make things easier. They in effect tell all browsers to load the phone optimized experience first, while keeping unnecessary elements from loading at all.
Heavier styles are applied only when your application or site senses that it’s on a bigger screen. And that’s okay, because typically, a bigger browser means you’re on a faster machine— with a better internet connection.
Welcome to a mobile first approach. Questions @arvindang.