Shim for getComputedStyle in old IEs

getComputedStylePropertyValue.js

(function(window, undefined){
        window.getComputedStylePropertyValue = function(el,cssProperty){
                if(!window.getComputedStyle){
                    if(document.defaultView && document.defaultView.getComputedStyle){
                        return document.defaultView.getComputedStyle.getPropertyValue(cssProperty);
                    }    
                    else{
                            var camelCasedCssProperty = getCamelCasedCssProperty(cssProperty);
                            if(el.currentStyle){
                                return el.currentStyle(camelCasedCssProperty);
                            }
                            else{
                                return el.style[camelCasedCssProperty];
                            }
                    }
                }
                else{
                        return window.getComputedStyle(el).getPropertyValue(cssProperty);
                }
                
        }

        function getCamelCasedCssProperty(cssProperty){
                return cssProperty.replace(/-([a-z])/g, function (g) { return g[1].toUpperCase() });
        }

})(this)

Neat, but your polyfill does not return a computed style but the declared CSS one instead. I'll work for a better version ;)