.size{
	width:200px;
	height:50px;
}
.parent1{
	margin:10px;
	padding:10px;
	border:1px solid #ccc;

	.child{
		position:relative;
		background-color:#080;
	}

	@media(max-width:600px){
		.child{
			background-color:#0f0;
		}
	}
}

.parent2{
	margin:10px;
	padding:10px;
	border:1px solid #ccc;

	.child{
		position:relative;
		background-color:#008;
	}

	@media(max-width:600px){
		.child{
			background-color:#00f;
		}
	}
}