Create 3 side by side panel in bootstrap

Question

How can i create 3 panels in bootstrap side by side? I try with this with out luck:

<div class="panel panel-default">
   <div class="panel-heading">Main panel</div>
    <div class="row">
        <div class="col-sm-4">
            <div class="panel panel-default">
                 <div class="panel-heading">panel 1</div>
            </div>
        </div>
        <div class="col-sm-6">
             <div class="panel panel-default">
                 <div class="panel-heading">panel 2</div>
            </div>
        </div>
        <div class="col-sm-2">
            <div class="panel panel-default">
                 <div class="panel-heading">panel 3</div>
            </div>
        </div>
    </div>
   </div>
</div>

Result:

Main panel
    PANEL 1 
    PANEL 2 
    PANEL 3

Answer 1

You could have to use col-lg-x col-md-x col-sm-x classes where x is the column number.

It is working fine for me after adding proper media width columns. You can check it http://bootply.com/98480 .

If you added col-sm-x classes only, then it will not apply to the devices where viewport is less than 768px.