mobile Mobile banner resizing

I use to be able to use  this code

@media screen and (max-width: 480px){ #thumbnail > img {    height: 120px !important;    left: 50% !important;    transform: translateX(-50%);    width: auto !important;}}

to resize the mobile banner images to shrink in size using 7.0

Unfortunately it does not work for 7.1 any one have a code that is working for the update or have any ideas how to resize banner images using media queries ?

Can you share link to your site?