Add parameters

gistfile1.css

@lightblue:#a9c6d2;

.cloudstyle(@bgColour, @border-radius){ // Here we add the parameters
   content: '';
   position: absolute;
   background: @bgColour;
   z-index: -1;
   .rounded(@border-radius);
} //every part of the Cloud has this style

#cloud {
   width: 350px;
   height: 120px;
   position: relative;
   margin: 120px auto 20px;
   background: @lightblue;    
   .rounded(100px);
}
#cloud:before {
.cloudstyle(#292929, 200px); //we use the mixin and we specify different values for the parameters
      width: 180px;
      height: 180px;
      top: -90px;
      right: 50px;
      
  }
#cloud:after{
      .cloudstyle(#d91656, 100px);//same here
     width: 100px;
      height: 100px;
      top: -50px;
      left: 50px;     
  }