1. include .css file with media attribute:
<link rel="stylesheet" href="responsive.css" media="screen and (max-width: 900px)">
2. @media query without
<link>
@media screen and (max-width: 900px) {
    /* conditional CSS */
}
by Valeri Tandilashvili
4 years ago
CSS
responsive design
Learn CSS
2
Pro tip: use ```triple backticks around text``` to write in code fences