Desktop first, 3-column flexbox block

Hello, coders! I'm happy to introduce you my project where I used @media for the first time. I know it's very simple but I'm proud that I'd overcome this fear of the @media. I've an issue after (max-width: 480px) breakpoint that my block doesn't center anymore and I can't understand why. I'm looking forward to all your critics and thanks for checking this out! Happy coding!