title: Nested Bootstrap layout with padding
body: <p>How can I create a nested Bootstrap layout with padding in one of the sections?</p>
  
  <p>An illustration is below. If I wrap <code>#main-container</code> in a Bootstrap div with <code>.span12</code>, it works. But that means that <code>#main-content</code> is now 40px thinner than the <code>.span12</code> width, which means I can't use the Boostrap grid inside of it. (For instance, it'd be great to make <code>#left-column</code> a <code>.span9</code> and <code>#right-column</code> a <code>.span3</code>, but I can't.)</p>
  
  <p>Is there a better way to create this layout?</p>
  
  <p><img src="https://i.stack.imgur.com/ekaFq.png" alt="Layout illustration"></p>