title: how to center form using bootstrap 4
body: <p>I just learned bootstrap and try to centered a form using bootstrap 4 but seems keep failing. I've try put container, margin auto, grid, etc but still failing.</p>
  
  <p>Here is the last code using bootstrap grid.</p>
  
  <pre><code>&lt;form class="col-lg-6 offset-lg-3"&gt;
      &lt;div class="row"&gt;
          &lt;input type="text" placeholder="Example input"&gt;
          &lt;span class="input-group-btn"&gt;
              &lt;button class="btn btn-primary"&gt;Download&lt;/button&gt;
          &lt;/span&gt;
      &lt;/div&gt;
  &lt;/form&gt;
  </code></pre>
  
  <p>and here is the link <a href="https://jsfiddle.net/artjia/emsw7t93/" rel="noreferrer">https://jsfiddle.net/artjia/emsw7t93/</a> </p>