Mobile-first design means building websites and apps to work great on phones...

https://www.bookmarkingqueen.win/mobile-first-design-means-building-your-app-or-website-for-phones-first-so-it

Mobile-first design means building websites and apps to work great on phones first. It focuses on fast loading, easy-to-tap buttons, and simple menus that fit small screens. This makes browsing quick and smooth, even on the go