title: Susy: change the number of columns according to screen size
body: <p>In the Compass/Sass plugin, <a href="http://susy.oddbird.net/" rel="nofollow">Susy</a>, you set the number of columns in the _base.scss file. </p>
  
  <p>For a desktop view, I like to have 12 columns. However, this is too many columns for a mobile view. Is there a way to change the number of columns for a mobile display?</p>
  
  <p>(I'm make a responsive web design, so both the desktop and the mobile versions of the site will share the same _base file).</p>
  
  <p>Thanks!</p>