title: change button style according to state angularjs
body: <p>I have a problem finding the way to style a button according to it's state.
  I have a question, and four answer tiles.</p>
  
  <p>each tiles is coded like this:</p>
  
  <pre><code>&lt;div class="button-default" ng-model="btn0" ng-click"evalAnswer(answer, btn0)"&gt;{{answer}}&lt;/div&gt;
  &lt;div class="button-default" ng-model="btn1" ng-click"evalAnswer(answer, btn1)"&gt;{{answer}}&lt;/div&gt;
  &lt;div class="button-default" ng-model="btn2" ng-click"evalAnswer(answer, btn2)"&gt;{{answer}}&lt;/div&gt;
  &lt;div class="button-default" ng-model="btn3" ng-click"evalAnswer(answer, btn3)"&gt;{{answer}}&lt;/div&gt;
  </code></pre>
  
  <p>On the controller side I have a function that, on click, look at the answer and return "good" if the answer is correct, and "nope" if the answer is not good.</p>
  
  <p>What I would like is to add button styling within these good and nope states so the button become red in case the answer is nope, and green if it's the good answer. I already created the class and I only need to change "button-default" to "button-good" or "button-wrong". Also, It needs to change only the clicked button. </p>
  
  <p>Any idea on the way to do that?</p>