Code:
//Ext.util.CSS.refreshCache();
Ext.util.CSS.getRule(".x-body");
TypeError: rules is null
Code:
        getRule: function(selector, refreshCache, rawCache) {
            var i;

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