.border-radius (@radius: 3px) {
    -webkit-border-radius: @radius;
    -moz-border-radius: @radius;
    border-radius: @radius;
  
    -moz-background-clip: padding;
    -webkit-background-clip: padding-box;
    background-clip: padding-box;
  }
  
  .opacity (@opacity: 0.5) {
    -webkit-opacity: @opacity;
    -moz-opacity: @opacity;
    opacity: @opacity;
  }