Bootstrap : Having two columns taking the full width but with a separator

Hey I am having the following html code :

<div class='col-sm-7 foo'>...</div>
<div class='col-sm-5 foo'>...</div>

and in my css:

.foo {
   background-color: white;
}

I can't add some margin between them as they are taking the full width due to bootstrap. Though I would like to add a separator between them (10px or so) with no background-color. How can I achieve this (I have to use bootstrap for other reasons).