title: How to centrally assign a same CSS class to multiple elements, such as when using frameworks like Bootstrap?
body: <p>I have just started studying web development and tried a couple of front-end frameworks such as Bootstrap, 960 and Foundation.</p>
  
  <p>For example with Bootstrap, when several images are to be universally assigned a same set of classes, for now I find it necessary that all these classes be placed within each elements individually, such as :</p>
  
  <pre><code>&lt;div id="foo" class="container"&gt;
      &lt;img src="img1.jpg" class="thumbnail img-responsive etc etc"/&gt;
      &lt;img src="img2.jpg" class="thumbnail img-responsive etc etc"/&gt;
      &lt;img src="img3.jpg" class="thumbnail img-responsive etc etc"/&gt;
      &lt;img src="img4.jpg" class="thumbnail img-responsive etc etc"/&gt;
      &lt;img src="img5.jpg" class="thumbnail img-responsive etc etc"/&gt;
  &lt;/div&gt;
  </code></pre>
  
  <p>Have anyone feel this inconvenient? I feel having to do this sort of steers away from the need which stylesheet emerges from: to <em>separate</em> style from structure and avoid repetition.</p>
  
  <p>I wish I could select all the <strong>img</strong> in <strong>#foo</strong>, and give all of them a same set of class.I believe there ought to be a way of doing this, only that I don't know. Any ideas folks?</p>