title: Apply class depending on media query screen size
body: <p>I am using Twitter Bootstrap. I have a <code>btn-group</code>. I want the <code>btn-group</code> and <code>btn-group-justified</code> classes added for screens at or above <code>768px</code>, and the <code>btn-group-vertical</code> class applied for screens at or below <code>767px</code>. How can I do this?</p>