[DvirCohen]

css

div {
   border: 1px solid black;
   margin: 4px;
   width: 100%;
}

.short1,
.short2 {
    float: left;
}

.short1 {
   width: 70%; 
}

.short2  {
    width: 30%;
}

html

<div>...</div> <!-- long div -->
<div class='short1'>...</div> <!--longest from the 2 middle divs -->
<div class='short2'>...</div> <!-- shortest from the 2 middle divs -->
<div>...</div> <!-- long div -->