1. First define two links, or you can have one, and then the CSS you want to change

<link rel="stylesheet" type="text/css" href="main.css" />
<link id="size-stylesheet" rel="stylesheet" type="text/css" href="narrow.css" />

2. The following JavaScript code will change CSS according to different browser sizes

function adjustStyle(width) {
    width = parseInt(width);
    if (width < 701) {
        $("#css").attr("href", "css/narrow.css");
    } else if ((width >= 701) && (width < 900)) {
        $("#css").attr("href", "css/medium.css");
    } else {
       //$("#css").attr("href", "<?php bloginfo('stylesheet_url'); ?>");
       document.write("css/style.css")
    }
}
$(function() {
    adjustStyle($(this).width());
    $(window).resize(function() {
        adjustStyle($(this).width());
    });
});

The above code has been tested available!!