#main-loading {
    position: relative;
    background-image: url('images/cdmx_aerea.jpg'); 
}

#main-loading #app-loading{
  position: absolute;
  background-repeat: no-repeat;
  top: 50%;
  left: 50%;
  transform: translate(-50%, -50%);
}

    #main-loading #loading-gif {
        position: absolute;
        background-image: url('images/busy-indicator.gif');
        background-repeat: no-repeat;
        width: 150px;
        height: 150px;
        top: 50%;
        left: 50%;
        transform: translate(-50%, -50%);
    }