title: Hamburger drop-down menu not working when page is in "mobile" size on desktop
body: <p>my hamburger button isn't working when I minimize the page to mobile size. Everything else seems to flow correctly, I've checked numerous times on the code and it seems to be correct. At this point, I'm not sure whether it's the script codes I have down below which disables the drop-down menu or what?</p>
  
  <pre><code>&lt;!DOCTYPE html&gt;
  &lt;html&gt;
  &lt;head&gt;
      &lt;title&gt;Image Gallery&lt;/title&gt;
      &lt;link rel="stylesheet" type="text/css" href="https://maxcdn.bootstrapcdn.com/bootstrap/3.3.7/css/bootstrap.min.css"&gt;
      &lt;link rel="stylesheet" type="text/css" href="gallery.css"&gt;
  &lt;/head&gt;
  &lt;body&gt;
      &lt;nav class="navbar navbar-inverse navbar-fixed-top"&gt;
          &lt;div class="container"&gt;
              &lt;div class="navbar-header"&gt;
                  &lt;button type="button" class="navbar-toggle collapsed" data-toggle="collapse" date-target="#bs-nav-demo" aria-expanded="false"&gt;
                      &lt;span class="sr-only"&gt;Toggle navigation&lt;/span&gt;
                      &lt;span class="icon-bar"&gt;&lt;/span&gt;
                      &lt;span class="icon-bar"&gt;&lt;/span&gt;
                      &lt;span class="icon-bar"&gt;&lt;/span&gt;
                  &lt;/button&gt;
                      &lt;a href="#" class="navbar-brand"&gt;&lt;span class="glyphicon glyphicon-picture" aria-hidden="true"&gt;&lt;/span&gt; IMAGES&lt;/a&gt;
              &lt;/div&gt;
          &lt;div class="collapse navbar-collapse" id="bs-nav-demo-1"&gt;
                  &lt;ul class="nav navbar-nav"&gt;
                      &lt;li&gt;&lt;a href="#"&gt;About&lt;/a&gt;&lt;/li&gt;
                      &lt;li&gt;&lt;a href="#"&gt;Contact&lt;/a&gt;&lt;/li&gt;
                  &lt;/ul&gt;
                  &lt;ul class="nav navbar-nav navbar-right"&gt;
                          &lt;li&gt;&lt;a href="#"&gt;Sign Up&lt;/a&gt;&lt;/li&gt;
                      &lt;li&gt;&lt;a href="#"&gt;Login&lt;/a&gt;&lt;/li&gt;
                  &lt;/ul&gt;
              &lt;/div&gt;  
          &lt;/div&gt;  
      &lt;/nav&gt;
  
  &lt;div class="container"&gt;
      &lt;div class="jumbotron"&gt;
          &lt;h1&gt;&lt;span class="fas fa-camera-retro"&gt;&lt;/span&gt; The Image Gallery&lt;/h1&gt;
          &lt;p&gt;Wonderful pictures at your disposal!&lt;/p&gt;
      &lt;/div&gt;
  
      &lt;div class="row"&gt;
          &lt;div class="col-lg-4 col-sm-6" &gt;
              &lt;div class="thumbnail"&gt;
                  &lt;img src="http://i.imgur.com/qK42fUu.jpg"&gt;
              &lt;/div&gt;  
          &lt;/div&gt;
          &lt;div class="col-lg-4 col-sm-6"&gt;
              &lt;div class="thumbnail"&gt;
                  &lt;img src="https://images.unsplash.com/photo-1435771112039-1e5b2bcad966?dpr=2&amp;fit=crop&amp;fm=jpg&amp;h=825&amp;q=50&amp;w=1450"&gt;
              &lt;/div&gt;  
          &lt;/div&gt;
          &lt;div class="col-lg-4 col-sm-6"&gt;
              &lt;div class="thumbnail"&gt;
                  &lt;img src="https://images.unsplash.com/photo-1442406964439-e46ab8eff7c4?dpr=2&amp;fit=crop&amp;fm=jpg&amp;h=825&amp;q=50&amp;w=1450"&gt;
              &lt;/div&gt;  
          &lt;/div&gt;
          &lt;div class="col-lg-4 col-sm-6"&gt;
              &lt;div class="thumbnail"&gt;
                  &lt;img src="https://images.unsplash.com/photo-1439524970634-649c37a69e5c?ixlib=rb-0.3.5&amp;q=80&amp;fm=jpg&amp;crop=entropy&amp;w=1450&amp;h=825&amp;fit=crop&amp;s=bfda9916c885869b43b70738693428d9"&gt;
              &lt;/div&gt;  
          &lt;/div&gt;
          &lt;div class="col-lg-4 col-sm-6"&gt;
              &lt;div class="thumbnail"&gt;
                  &lt;img src="https://images.unsplash.com/photo-1444090542259-0af8fa96557e?dpr=2&amp;fit=crop&amp;fm=jpg&amp;h=825&amp;q=50&amp;w=1450"&gt;
              &lt;/div&gt;  
          &lt;/div&gt;
          &lt;div class="col-lg-4 col-sm-6"&gt;
              &lt;div class="thumbnail"&gt;
                  &lt;img src="https://images.unsplash.com/photo-1434543177303-ef2cc7707e0d?dpr=2&amp;fit=crop&amp;fm=jpg&amp;h=825&amp;q=50&amp;w=1450"&gt;
              &lt;/div&gt;  
          &lt;/div&gt;
          &lt;div class="col-lg-4 col-sm-6"&gt;
              &lt;div class="thumbnail"&gt;
                  &lt;img src="https://images.unsplash.com/photo-1436262513933-a0b06755c784?dpr=2&amp;fit=crop&amp;fm=jpg&amp;h=825&amp;q=50&amp;w=1450"&gt;
              &lt;/div&gt;  
          &lt;/div&gt;
          &lt;div class="col-lg-4 col-sm-6"&gt;
              &lt;div class="thumbnail"&gt;
                  &lt;img src="https://images.unsplash.com/photo-1439396087961-98bc12c21176?dpr=2&amp;fit=crop&amp;fm=jpg&amp;h=825&amp;q=50&amp;w=1450"&gt;
              &lt;/div&gt;  
          &lt;/div&gt;
          &lt;div class="col-lg-4 col-sm-6"&gt;
              &lt;div class="thumbnail"&gt;
                  &lt;img src="https://images.unsplash.com/photo-1439694458393-78ecf14da7f9?dpr=2&amp;fit=crop&amp;fm=jpg&amp;h=825&amp;q=50&amp;w=1450"&gt;
              &lt;/div&gt;  
          &lt;/div&gt;
      &lt;/div&gt;      
  &lt;/div&gt;  
  
  &lt;script defer src="https://use.fontawesome.com/releases/v5.0.6/js/all.js"&gt;&lt;/script&gt;
  &lt;script src="https://code.jquery.com/jquery-3.3.1.js"&gt;&lt;/script&gt;
  &lt;script src="https://stackpath.bootstrapcdn.com/bootstrap/4.1.1/js/bootstrap.min.js"&gt;&lt;/script&gt;
  &lt;/body&gt;
  &lt;/html&gt;
  </code></pre>