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

div div {
	background: blue;
    position: absolute;

    height: 50px;
    width: 50px;
}
</style>
<div class=container><div style="top: 10px; bottom: 10px;"></div></div>
<div class=container><div style="left: 10px; right: 10px"></div></div>