Show the menu with a fade transition ?

I tried using `CSSTransitionGroup` like so:

```

{musicMenuItems}

```

`test` class definitions:

```
.test-enter {
opacity: 0.01;
}

.test-enter.test-enter-active {
opacity: 1;
transition: opacity 500ms ease-in;
}

.test-leave {
opacity: 1;
}

.test-leave.test-leave-active {
opacity: 0.01;
transition: opacity 300ms ease-in;
}
```

This doesn't work. Any idea how to show the menu with a fade animation?