To set div vertical align middle (valign) you need add few css style to main div

In the head

<style>
.main_div{
height:200px
width:500px;
display:table-cell;
vertical-align:middle;
border:1px solid #000000;
}
.block_div{
height:100px;
width:200px;
border:1px solid #000000;
}
</style>

In the body

<div class="main_div">
<div class="block_div">This is middle div</div>
</div>

To set vertical-align bottom of the div, just change the value of vertical-align in class main_div, there should be vertical-align:bottom;