Convert / extract all applied styles in DOM element convert it into inline css

css-utils.js

function getCss( elem ){
    var rules = [].slice.call(window.getMatchedCSSRules( elem ));
    return rules.map( rule => rule.style.cssText ).join('');
}

function addInlineCss( elem, isRecurssive ){
    elem.setAttribute( 'style', getCss( elem ) );

    if( isRecurssive && elem.children.length ){
        [].slice.call( elem.children ).forEach( v => addInlineCss(v, true ) )
    }
}