js/theme.js
function getStyleComputedProperty(element, property) {
    if (element.nodeType !== 1) {
      return [];
    } // NOTE: 1 DOM access here


    var window = element.ownerDocument.defaultView;
    var css = window.getComputedStyle(element, null);
    return property ? css[property] : css;
  }
function getStyleComputedProperty(element, property) {
    if (element.nodeType !== 1) {
      return [];
    } // NOTE: 1 DOM access here


    var window = element.ownerDocument.defaultView;
    var css = window.getComputedStyle(element, null);
    return property ? css[property] : css;
  }
Get CSS computed property of the given element
@method
@memberof Popper.Utils
@argument {Eement} element
@argument {String} property