Mobile-first design means creating apps and websites that work best on your...

https://wiki-tonic.win/index.php/What_Does_%E2%80%9CSecurity_Must_Remain_Invisible%E2%80%9D_Mean_in_UX_Terms%3F

Mobile-first design means creating apps and websites that work best on your phone from the start. It loads fast, so you don’t waste time waiting. Buttons and links are big and easy to tap with your fingers