'z-index' is not working

[gogo-boot]

Hi,

I appriciate this emil.

I have tried to set z-index, but it shows css error.
Am I doing wrong or ?

emile('test2', 'left:300px;z-index:4;padding:10px;border:50px solid #ff0000', {
duration: 500,
after: function(){
emile('test1', 'background:#0f0;left:100px;padding-bottom:100px;opacity:1', {
duration: 4000, easing: bounce
});
}
});