title: Changing icons when collapse is active (bootstrap accordion)
body: <p>I have something like this: </p>
  
  <pre><code>&lt;div class="panel-group" id="accordion"&gt;
                &lt;div class="panel panel-default"&gt;
                  &lt;div class="panel-heading"&gt;
                    &lt;h4 class="panel-title"&gt;
                      &lt;a data-toggle="collapse" data-parent="#accordion" href="#collapse1"&gt;
                      &lt;img class="icons" src="img/photography.png"&gt;
                      &lt;img class="unactive" src="img/arrow.png"&gt;
                      &lt;/a&gt;
                    &lt;/h4&gt;
                  &lt;/div&gt;
                  &lt;div id="collapse1" class="panel-collapse collapse in"&gt;
                    &lt;div class="panel-body collapse-text"&gt;text.&lt;/div&gt;
                  &lt;/div&gt;
                &lt;/div&gt;
  </code></pre>
  
  <p>And I want to change my icon which is class <code>unactive</code> to tranform: rotate 180deg when collapse is 'active'? Is it possible to do this using only CSS?</p>
  
  <p>PS. I found many similar topics but I really haven't found any useful informations.</p>