Looking for equal margins on top and bottom? Here's how to achieve it:
If you have a container div like this:
<div id="search">
<input id="txtSearch" type="txt">
</div>
Your CSS should look something like this:
#search{
min-width: 25%;
}
#txtSearch{
display: block;
width: 80%;
height: 60%;
margin: 0 auto;
}
To see the code in action, check out my JSFIDDLE link.