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                <div class="container">  
  <div class="row">
    <div class="column">
      <div class="my-content"></div>
    <div class="column">
      <div class="my-content"></div>
    <div class="column">
      <div class="my-content"></div>

<div>Column width: <span id="output"></span>px</div>


                .column {
  float: left;
  box-sizing: border-box;
  width: 33.3333333%;
  padding: 0 4px;

.container {
  padding: 8px 3%;
  background-color: gray;

.row {
  margin-left: -8px;
  margin-right: -8px;
  overflow: hidden;

.my-content {
  height: 40px;
  background-color: rgb(220, 220, 220);


                var HAS_COMPUTED_STYLE = !!window.getComputedStyle;
var getStyles = window.getComputedStyle || function() {};

    return false;

  var parent = document.body || document.documentElement;
  var e = document.createElement('div'); = 'width:10px;padding:2px;' +

  var width = getStyles(e, null).width;
  var ret = width === '10px';


  return ret;

 * Retrieve the computed style for an element, parsed as a float.
 * @param {Element} element Element to get style for.
 * @param {string} style Style property.
 * @param {CSSStyleDeclaration} [styles] Optionally include clean styles to
 *     use instead of asking for them again.
 * @return {number} The parsed computed value or zero if that fails because IE
 *     will return 'auto' when the element doesn't have margins instead of
 *     the computed style.
var getNumberStyle = function(element, style, styles) {
    styles = styles || getStyles(element, null);
    var value = getFloat(styles[style]);

    // Support IE<=11 and W3C spec.
    if (!COMPUTED_SIZE_INCLUDES_PADDING && style === 'width') {
      value += getFloat(styles.paddingLeft) +
        getFloat(styles.paddingRight) +
        getFloat(styles.borderLeftWidth) +
    } else if (!COMPUTED_SIZE_INCLUDES_PADDING && style === 'height') {
      value += getFloat(styles.paddingTop) +
        getFloat(styles.paddingBottom) +
        getFloat(styles.borderTopWidth) +

    return value;
  } else {
    return getFloat($(element).css(style));

var isNumber = function(n) {
	return !isNaN(parseFloat(n)) && isFinite(n);

var getFloat = function(value) {
  value = parseFloat(value);
  return isNumber(value) ? value : 0

function showWidth() {
  var output = document.querySelector('#output');
  var column = document.querySelector('.column');
  output.textContent = getNumberStyle(column, 'width');

window.addEventListener('resize', showWidth);