Add CSS styles to a webpage.

add-stylesheet.js

function addCss(rule) {
    // https://stackoverflow.com/a/38063486
    let css = document.createElement('style');
    css.type = 'text/css';
    if (css.styleSheet) {
        css.styleSheet.cssText = rule; // Support for IE
    }
    else {
        css.appendChild(document.createTextNode(rule)); // Support for the rest
    }
    document.getElementsByTagName("head")[0].appendChild(css);
}


// How to use.
var rules = '#wrap, #about {background: #bcd6f7;} #wrap .lines div {color: #94a9c3;}';
addCss(rules);