title: Sass/Rails form validation with Bootstrap 3
body: <p>I've got a form and when it's not filled out properly, Rails wraps it in a "field_with_errors" class. I've got a css.scss file in which I import Bootstrap, and I want to extend field_with_errors to use Bootstrap 3's form validation styling. I found this</p>
  
  <pre><code>.field_with_errors {
      @extend .control-group;
      @extend .error;
  }
  </code></pre>
  
  <p><br/>
  But it didn't work, so I figured out that the classes were Bootstrap 2 classes. So I found their equivalents:</p>
  
  <pre><code>.field_with_errors {
      @extend .form-group;
      @extend .has-error;
  }
  </code></pre>
  
  <p><br/>
  But this doesn't seem to have any effect. I'm completely new to Rails and Sass, can somebody give me a pointer? </p>