#container {
    height: 300px;
    .div {
        width: 30px;
        background-color: blue;
    }
}
ul#footer {
    list-style: none;
}

/*
    Turns into:
*/

#container {
    height: 300px;
}
#container .div {
    width: 30px;
    background-color: blue;
}
ul#footer {
    list-style: none;
}