title: The search box and an additional button not aligned in a navbar
body: <p>I have a navbar. inside it I have a search form and an additional button. The problem is that the button not aligned with other elements in the navbar: 
  <img src="https://i.stack.imgur.com/K66o7.png" alt="enter image description here"></p>
  
  <p>Here is my code. Anyone sees why they shouldn't be aligned? </p>
  
  <pre><code>&lt;html&gt; 
      &lt;head&gt; 
          &lt;title&gt;Bootstrap 3 &lt;/title&gt;
          &lt;link href ="css/bootstrap.css" rel = "stylesheet"&gt;
          &lt;link href ="css/bootstrap.min.css" rel = "stylesheet"&gt;
          &lt;link href ="css/bootstrap-theme.min.css" rel = "stylesheet"&gt;
          &lt;link href ="css/styles.css" rel = "stylesheet"&gt;
  
          &lt;script src="http://code.jquery.com/jquery-1.11.2.min.js"&gt;&lt;/script&gt;
          &lt;script src="js/bootstrap.min.js"&gt;&lt;/script&gt;
      &lt;/head&gt; 
      &lt;body&gt; 
  
          &lt;nav class="navbar navbar-default"&gt;
  
            &lt;div class="container-fluid"&gt;
  
              &lt;div class="navbar-header"&gt;
  
          &lt;!-- box --&gt;
          &lt;form class="navbar-form navbar-left" role="search"&gt;
            &lt;div class="form-group"&gt;
              &lt;input type="text" class="form-control" placeholder="Search"&gt;
            &lt;/div&gt;
            &lt;button type="submit" class="btn btn-default"&gt;Submit&lt;/button&gt;
          &lt;/form&gt;
  
              &lt;/div&gt;
  
          &lt;!-- Single button --&gt;
          &lt;div class="btn-group"&gt;
            &lt;button type="button" class="btn btn-default dropdown-toggle" data-toggle="dropdown" aria-expanded="false"&gt;
              Action &lt;span class="caret"&gt;&lt;/span&gt;
            &lt;/button&gt;
            &lt;ul class="dropdown-menu" role="menu"&gt;
              &lt;li&gt;&lt;a href="#"&gt;Action&lt;/a&gt;&lt;/li&gt;
              &lt;li&gt;&lt;a href="#"&gt;Another action&lt;/a&gt;&lt;/li&gt;
              &lt;li&gt;&lt;a href="#"&gt;Something else here&lt;/a&gt;&lt;/li&gt;
              &lt;li class="divider"&gt;&lt;/li&gt;
              &lt;li&gt;&lt;a href="#"&gt;Separated link&lt;/a&gt;&lt;/li&gt;
            &lt;/ul&gt;
          &lt;/div&gt;
  
            &lt;/div&gt;
  
          &lt;/nav&gt;
  
      &lt;/body&gt; 
  &lt;/html&gt;
  </code></pre>