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

https://echo-wiki.win/index.php/What_is_a_CDN_and_Do_I_Need_One_for_a_Small_Site%3F

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