<div id="myDiv"
style="position:absolute;
left:168px;
top:251px;
width:192px;
height:66px;
z-index:1;
background-color:red;">
an z-index of 1.
</div>
<div style="position:absolute;
left:168px;
top:251px;
z-index:12;
height:50;
background-color:blue;">
a z-index of 12.
</div>
<button onclick="myDiv.style.zIndex = 20;">
Bring red to front
</button>