Nested Rules example css

gistfile1.css

#cloud {
   width: 350px;
   height: 120px;
   background: #a9c6d2;    
   border-radius: 100px;
   -webkit-border-radius: 100px;
   -moz-border-radius: 100px;
   position: relative;
   margin: 120px auto 20px;
}

#cloud:after, #cloud:before {
   content: '';
   position: absolute;
   background: #a9c6d2;
   z-index: -1
}

#cloud:after {
   width: 100px;
   height: 100px;
   top: -50px;
   left: 50px;
   border-radius: 100px;
   -webkit-border-radius: 100px;
   -moz-border-radius: 100px;
}

#cloud:before {
   width: 180px;
   height: 180px;
   top: -90px;
   right: 50px;
   border-radius: 200px;
   -webkit-border-radius: 200px;
   -moz-border-radius: 200px;
}