JSFiddle - React, Tailwind, and code Playground

HTML

<div id="test">
    This is a test div with margin:5px auto
</div>

<div id="list">
    <div class="listitem">List item 1</div>
    <div class="listitem">List item 2</div>
    <div class="listitem">List item 3</div>
    <div class="listitem">List item 4</div>  
</div>

CSS

#test, .listitem{margin:5px auto; width:50%; border:1px solid black; padding:20px}

JavaScript

function css(a){
    var sheets = document.styleSheets, o = {};
    for(var i in sheets) {
        var rules = sheets[i].rules || sheets[i].cssRules;
        for(var r in rules) {
            if(a.is(rules[r].selectorText)) {
                o = $.extend(o, css2json(rules[r].style), css2json(a.attr('style')));
            }
        }
    }
    return o;
}

function css2json(css){
        var s = {};
        if(!css) return s;
        if(css instanceof CSSStyleDeclaration) {
            for(var i in css) {
                if((css[i]).toLowerCase) {
                    s[(css[i]).toLowerCase().replace('-value', '')] = (css.getPropertyValue(css[i]));
                }
            }
        } else if(typeof css == "string") {
            css = css.split("; ");          
            for (var i in css) {
                var l = css[i].split(": ");
                s[l[0].toLowerCase()] = (l[1]);
            };
        }
        return s;
    }

cssObj = css($("#test"));  //css object for element #test
console.log(cssObj);
$("#test").after("margin-left is " + (cssObj['margin-left'] || cssObj['margin-left-value']) + '<br/>');
$("#test").after("margin-right is " + cssObj['margin-right'] + '<br/>');
$("#test").after("margin-top is " + cssObj['margin-top'] + '<br/>');
$("#test").after("margin-bottom is " + cssObj['margin-bottom'] + '<br/>');


$(".listitem").each(function(index, element){
    listobj = css($(element));
    $(element).after("margin-left is " + listobj['margin-left'] + '<br/>');
    $(element).after("margin-right is " + listobj['margin-right'] + '<br/>');
    $(element).after("margin-top is " + listobj['margin-top'] + '<br/>');
    $(element).after("margin-bottom is " + listobj['margin-bottom'] + '<br/>');
});