Resizing gif for mobile

Site URL: https://www.handford.com/

Hi, 

My gif is resizing for mobile version of site on these pages: 

https://www.handford.com/imaging

https://www.handford.com/creative

I've tried adding this code but doesn't seem to be doing the trick: 

<style>

@media screen and (max-width:640px) {
.homepage .section-background image {
    width: 100% !important;
    height: auto !important;
}

</style>

Also would like to decrease the padding around the text in between the gif and the photo beneath. 

Thanks in advance!