HTML and raw CSS

Curious about the use case of max-width and width of certain elements, especially in the case of building responsive websites. In this specific challenge, I made had the qr code card itself be a width of 100% and a max width of 300px, so when the device size was getting smaller the card would stay the same size (100 percent of the width of the container) and once the device size is large (desktop etc) it would stay at a max of 300px. Is this an acceptable usage of these CSS properties?