<style>
.container {
	border: 5px solid green;
    height: 100px;
    width: 100px;
    position: relative;
}

div div {
	background: blue;
    position: absolute;

    height: 50px;
    width: 50px;

    top: 10px;
    bottom: 10px;
}
</style>
<div class=container><div style="margin-top: auto;"></div></div>
<div class=container><div style="margin-bottom: auto;"></div></div>
<div class=container><div style="margin-top: auto; margin-bottom: auto;"></div></div>