One possible could be like this,
HTML
<div class="box-left-mini">
<div class="front">this div is infront</div>
<div class="behind">
this div is behind
</div>
</div>
CSS
.box-left-mini{
float:left;
background-image:url(website-content/hotcampaign.png);
width:292px;
height:141px;
}
.front{
background-color:lightgreen;
}
.behind{
background-color:grey;
position:absolute;
width:100%;
height:100%;
top:0;
z-index:-1;
}
But it really depends on the layout of your div elements i.e. if they are floating, or absolute positioned etc.