codice:
.HEADER {
background-color: #E8E8E8;
width: 100%;
height: 50px;
border: 0.5pt dashed #0A50A1;
}
.BOX1 {
width: 100%;
height: 100px;
background-color: #FFFFFF;
border: 0.5pt dashed #0A50A1;
margin: 2px 0px;

}
.FOOTER{
background-color: #E8E8E8;
width: 100%;
height: 50px;
border: 0.5pt dashed #0A50A1;
}
.SX{
width:20%;
height:100%;
background-color:#000080;
float:left;
}
.DX{
width:20%;
height:100%;	
background-color:#000080;
float:right;
}
.CENTRO{
width:100%;
height:100%;	
background-color:#990000;
}
nel body:
codice:
....
<div class="BOX1">
<div class="SX"></div>
<div class="DX"></div>
<div class="CENTRO"></div>
</div>
....