title: Bootstrap 3 input group
body: <p>Now I'm working with bootstrap 3 input group, but the result is not like expectation.
  i want make select [input]-[input text]-[button] in one line.
  but in my case button have white space inside like this
  <a href="https://i.stack.imgur.com/97MsA.jpg" rel="nofollow noreferrer">Input Group SS</a>.
  this is my code:</p>
  
  <p><div class="snippet" data-lang="js" data-hide="false" data-console="true" data-babel="false">
  <div class="snippet-code">
  <pre class="snippet-code-html lang-html prettyprint-override"><code>&lt;div class="card-block bg-white"&gt;
          &lt;div class="row"&gt;
           &lt;form action="&lt;?php echo base_url(); ?&gt;performance" method="post"&gt;
              &lt;div class="form-group"&gt;
               &lt;div class="input-group col-md-6 col-md-offset-4 col-sm-12 col-xs-12"&gt;
                   &lt;span class="input-group-btn"&gt;
                   &lt;select class="form-control input-sm" name="id_cabang" id="id_cabang"&gt;
                            &lt;option&gt;Option 1&lt;/option&gt;
                            &lt;option&gt;Option 2&lt;/option&gt;
                            &lt;option&gt;Option 3&lt;/option&gt;
                      &lt;/select&gt;
                      &lt;/span&gt;
                      &lt;span class="input-group-btn"&gt;
                       &lt;input id="bulan_kinerja" name="bulan_kinerja" type="text" class="form-control input-sm bln_picker" data-provide="datepicker" placeholder="Datepicker" value="&lt;?php echo $bulan_kinerja; ?&gt;"/&gt;
                      &lt;/span&gt;
                      &lt;span class="input-group-btn"&gt;
                      &lt;button type="submit" class="btn btn-primary btn-sm" id="kinerja_btn"&gt;Submit&lt;/button&gt;
                      &lt;/span&gt;
                  &lt;/div&gt; 
               &lt;/div&gt; 
               &lt;/form&gt;
          &lt;/div&gt;
      &lt;/div&gt;</code></pre>
  </div>
  </div>
  </p>
  
  <p>I had tried some example in google but some case, if the screen width changes smaller, it turns to new line.</p>
  
  <p>I want the result is full of responsive width and pure using bootstrap 3 class. please help. thanks so much.</p>