LESS vs CSS

less.css

/* less file */
.my_mixin {
	display: block; 
	text-indent: -9999em; 
	background-color: transparent; 
	background-position: 0 0; 
	background-repeat: no-repeat; 
	overflow: hidden; 
}
h1 a, .pagination em, .cog a { 
	.my_mixin
}

/* css file */
.my_mixin {
  display: block;
  text-indent: -9999em;
  background-color: transparent;
  background-position: 0 0;
  background-repeat: no-repeat;
  overflow: hidden;
}
h1 a, .pagination em, .cog a {
  display: block;
  text-indent: -9999em;
  background-color: transparent;
  background-position: 0 0;
  background-repeat: no-repeat;
  overflow: hidden;
}