Huddle landing page with a single introductory section with HTML & CSS

Hi, it's my first challenge on Frontend Mentor, so I'll be very greatfull for your feedback!

I fixed issue with icons, thanks to Elaine (@elaineleung).

Now I wondering what is the best practice to switch between desktop design and mobile design. In this solution, I do it when the window width becomes less than 575px. And I'm wondering if there is a best practice for this or if it always depends on the design.

Thank you! Amir