Answers for "js css file"

javascript css link append

document.getElementsByTagName("head")[0].insertAdjacentHTML(
    "beforeend",
    "<link rel=\"stylesheet\" href=\"path/to/style.css\" />");

append css file with javascript

var cssFile = document.createElement('link');
    cssLink1.rel = 'stylesheet';
    cssLink1.href = "styles.css";  // or path for file {themes('/styles/mobile.css')}
    document.head.appendChild(cssFile); // append css to head element