правая сторона дивия
#wrapper{
background:red;
overflow:auto;
}
#c1{
float:left;
background:blue;
}
#c2{
background:green;
float:right;
}
<div id="wrapper">
<div id="c1">con1</div>
<div id="c2">con2</div>
</div>
Prickly Porcupine