title: Bold the paragraph after clicked
body: <pre><code>&lt;div id="box"&gt;
  &lt;p class="b"&gt;item 1&lt;/p&gt;
  &lt;p class="b"&gt;item 2&lt;/p&gt;
  &lt;p class="b"&gt;item 3&lt;/p&gt;
  &lt;p class="b"&gt;item 4&lt;/p&gt;
  &lt;p class="b"&gt;item 5&lt;/p&gt;
  &lt;/div&gt; 
  </code></pre>
  
  <p>How to bold the selected paragraph after clicked? 
  For example, if I click 'item 2', only the item 2 will bold after I clicked</p>