make mobile background smaller

I found custom code and used it for the background color of the entire site, but I need it smaller on mobile and iPad view. How can I have separate sizes?

body { border-left:70px solid #529fbb; }
body { border-right:70px solid #529fbb; }
body { border-top:20px solid #529fbb; }
body { border-bottom:6px solid #529fbb; }

Use this code

@media screen and (max-width:991px) {
body { 
	border-left:10px solid #529fbb !important; 
}
}