two ways to append a stylesheet reference to the head

cssAppendToHead.js

//
// Script for adding external CSS stylesheet to DXP
//

var myStylesLocation = 'http://www.ecwincentives.com/assets/css/bootstrap.min.css'

$('<link rel="stylesheet" type="text/css" href="'+myStylesLocation+'" >')
   .appendTo("head");


//
// Alternate way to add css resource
//

//add css to head
$("<link/>", { "rel": "stylesheet", "type": "text/css", "href": "https://ajax.aspnetcdn.com/ajax/jquery.dataTables/1.9.4/css/jquery.dataTables.css" }).appendTo("head");