title: Bootstrap input button not aligning with other fields
body: <p><a href="https://i.stack.imgur.com/bgBYP.png" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/bgBYP.png" alt="a busy cat"></a><br>
  <sub>(source: <a href="http://bryancorrell.com/FilterButton.PNG" rel="nofollow noreferrer">bryancorrell.com</a>)</sub>  </p>
  
  <p>I was able fix the alignment issue, but then I lose the rounded corners on the inputs and can't figure out how to get them back. See the link below:</p>
  
  <p><a href="https://jsfiddle.net/yzw8q28q/5/" rel="nofollow noreferrer">https://jsfiddle.net/yzw8q28q/5/</a></p>
  
  <pre><code>&lt;form class="simple_form form-inline" novalidate="novalidate" action="/dashboard/school" accept-charset="UTF-8" method="get"&gt;
    &lt;div class="form-group select required filter_discipline_id"&gt;
      &lt;select class="select required form-control" placeholder="Discipline" name="filter[discipline_id]" id="filter_discipline_id"&gt;
        &lt;option value=""&gt;- Discipline -&lt;/option&gt;
        &lt;option selected="selected" value="1"&gt;HW&lt;/option&gt;
        &lt;option value="2"&gt;SW&lt;/option&gt;
      &lt;/select&gt;
    &lt;/div&gt;
    &lt;div class="form-group"&gt;
      &lt;input type="submit" name="commit" value="Filter" class="btn btn-default btn btn-primary form-control" /&gt;
    &lt;/div&gt;
  &lt;/form&gt;
  
  &lt;br /&gt;&lt;hr /&gt;&lt;br /&gt;
  
  &lt;div class="input-group"&gt;
    &lt;form class="simple_form form-inline" novalidate="novalidate" action="/dashboard/school" accept-charset="UTF-8" method="get"&gt;
      &lt;div class="form-group select required filter_discipline_id"&gt;
        &lt;select class="select required form-control" placeholder="Discipline" name="filter[discipline_id]" id="filter_discipline_id"&gt;
          &lt;option value=""&gt;- Discipline -&lt;/option&gt;
          &lt;option selected="selected" value="1"&gt;HW&lt;/option&gt;
          &lt;option value="2"&gt;SW&lt;/option&gt;
        &lt;/select&gt;
      &lt;/div&gt;
      &lt;div class="form-group"&gt;
        &lt;input type="submit" name="commit" value="Filter" class="btn btn-default btn btn-primary form-control" /&gt;
      &lt;/div&gt;
    &lt;/form&gt;
  &lt;/div&gt;
  </code></pre>
  
  <p>Ruby Code that's generating the HTML form:</p>
  
  <pre><code>&lt;%= minimal_form_for :filter, url: @form_path, method: :get, html: {class: 'form-inline' } do |f| %&gt;
  &lt;%= f.error_notification %&gt;
  &lt;%= f.input :discipline_id, 
    collection: Discipline.all, 
    include_blank: '- Discipline -', 
    selected: params[:discipline_id] %&gt;
  &lt;div class="form-group"&gt;
      &lt;%= f.button :submit, 'Filter', class: "btn-primary form-control" %&gt;
  &lt;/div&gt;
  </code></pre>
  
  <p>It looks like simple_form is injecting the "btn" class. Not sure how to stop that.</p>