How to resize the logo and header featured image for mobile screens

hi everyone, i am trying to change the size of the logo and the featured header image for sreens smaller than 765px because both images are to close from each other on mobile devices. I tried to add in the css : @media all and (max-width: 480px) { .custom-logo .site-header-logo { max-width: 100px; height: 100px; } } But it doesn't change anything. It would e great if someone could help me ! Thank you :) Maud