title: Using Blueprint CSS, how do we style 3 columns, each 300px wide, with 15px margins or paddings in between?
body: <p>The width of the content-area is 960px, with 3 columns, each 300px, so total 900px, and with padding / margin of 15px between columns, which is total 30px,
  and finally, to the left of 1st column there should be 15px padding / margin, and to the right of the 3rd column, the same.  So total is also 30px.</p>
  
  <p>900px + 30px + 30px will be 960px.</p>
  
  <p>How to do that in Blueprint / CSS?   This can be done using simple CSS, but the coding standard requires using Blueprint CSS.</p>