<div class="ptest">
        <div class="ptest-inner">
        </div>
	</div>
.ptest {
  width: 200px;
  position: relative;
  height: 0;
  padding-bottom: 60%;
}
.ptest-inner {
    position: absolute;
    top: 0;
    left: 0;
    right: 0;
    bottom: 0;
    background: #333;
}

	<div class="ptest">
		<div class="ptest-wrap">
			<div class="ptest-inner">
			</div>
		</div>
	</div>
.ptest {
  width: 200px;
  position: relative;
}

.ptest-wrap {
    padding-top: 60%;
}
.ptest-inner {
    position: absolute;
    top: 0;
    left: 0;
    right: 0;
    bottom: 0;
    background: #333;
}

https://stackoverflow.com/questions/8894506/can-i-scale-a-divs-height-proportionally-to-its-width-using-css