Gets an an individual CSS rule by selector(s)
@param {String/String[]} selector The CSS selector or an array of selectors to try. The first selector that is found is returned.
@param {Boolean} refreshCache true to refresh the internal cache if you have recently updated any rules or added styles dynamically
@return {CSSStyleRule} The CSS rule or null if one is not found
function(selector, refreshCache, rawCache) {
            var i, result;

            if (!rules || refreshCache) {
                CSS.refreshCache();
            }
            if (!Ext.isArray(selector)) {
                result = rules[selector.toLowerCase()]
                if (result && !rawCache) {
                    result = result.cssRule;
                }
                return result || null;
            }
            for (i = 0; i < selector.length; i++) {
                if (rules[selector[i]]) {
                    return rawCache ? rules[selector[i].toLowerCase()] : rules[selector[i].toLowerCase()].cssRule;
                }
            }
            return null;
        }