title: Bootstrap 4 not centering vertically
body: <p>Something really strange happening, I am using the right classes and style to center my h1 and paragraph. The div with my col-12 that contains the H1 and the other col-12 that contains the paragraph should be close one to another in the center of the Row div.</p>
  
  <p>Why it is not working even tho I am using justify-content center and align-items center? Thank you!</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-css lang-css prettyprint-override"><code>    *{
       margin: 0;
       padding: 0;
       box-sizing: border-box;
      }
      
      body{
       background-color: pink;
      }
      
      .red-b{border: 4px solid red;}
      .blue-b{border: 4px solid blue;}
      .yellow-b{border: 4px solid yellow;}
      .green-b{border: 4px solid green;}
      .orange-b{border: 4px solid orange;}
      .black-b{border: 4px solid black;}
      
      /* HEADER */
      
      .main-header{
       background-image: url('header-photo.jpg');
       height: 100vh;
       background-size: cover;
       background-repeat: no-repeat;
       background-position: center center;
      }
      
      
      
      .main-header a{
       color: #fff;
      }
      
      .header-banner{
       height: 80vh;
      }
      
      h1{
       color: white;
       font-size: 100px;
       text-align: center;
       font-weight: 700;
      }
      
      @media only screen and (max-width: 1200px) {
                  
       h1{
        color: red;
       }
      }
      
      @media only screen and (max-width: 992px) {
       h1{
        color: yellow;
        font-size: 70px;
       }
      }
      
      /*MAIN*/
      
      /*FOOTER*/</code></pre>
  <pre class="snippet-code-html lang-html prettyprint-override"><code>&lt;!doctype html&gt;
      &lt;html lang="en"&gt;
        &lt;head&gt;
          &lt;!-- Required meta tags --&gt;
          &lt;meta charset="utf-8"&gt;
          &lt;meta name="viewport" content="width=device-width, initial-scale=1, shrink-to-fit=no"&gt;
      
          &lt;!-- Bootstrap CSS --&gt;
          &lt;link rel="stylesheet" href="https://maxcdn.bootstrapcdn.com/bootstrap/4.0.0/css/bootstrap.min.css" integrity="sha384-Gn5384xqQ1aoWXA+058RXPxPg6fy4IWvTNh0E263XmFcJlSAwiGgFAW/dAiS6JXm" crossorigin="anonymous"&gt;
      
          &lt;title&gt;Hello, world!&lt;/title&gt;
      
          &lt;link rel="stylesheet" type="text/css" href="style.css"&gt;
        &lt;/head&gt;
        &lt;body&gt;
          &lt;header class="main-header"&gt;
          &lt;div class="container"&gt;
            &lt;nav class="navbar navbar-expand-lg navbar-dark"&gt;
              &lt;a class="navbar-brand" href="#"&gt;START BOOTSTRAP&lt;/a&gt;
              &lt;button class="navbar-toggler" type="button" data-toggle="collapse" data-target="#navbarSupportedContent" aria-controls="navbarSupportedContent" aria-expanded="false" aria-label="Toggle navigation"&gt;
                &lt;span class="navbar-toggler-icon"&gt;&lt;/span&gt;
              &lt;/button&gt;
      
              &lt;div class="collapse navbar-collapse" id="navbarSupportedContent"&gt;
                &lt;ul class="navbar-nav ml-auto"&gt;
                  &lt;li class="nav-item active"&gt;
                    &lt;a class="nav-link" href="#"&gt;About &lt;span class="sr-only"&gt;(current)&lt;/span&gt;&lt;/a&gt;
                  &lt;/li&gt;
                  &lt;li class="nav-item"&gt;
                    &lt;a class="nav-link" href="#"&gt;Services&lt;/a&gt;
                  &lt;/li&gt;
                  &lt;li class="nav-item"&gt;
                    &lt;a class="nav-link" href="#"&gt;Portfolio&lt;/a&gt;
                  &lt;/li&gt;
                  &lt;li class="nav-item"&gt;
                    &lt;a class="nav-link" href="#"&gt;Contact&lt;/a&gt;
                  &lt;/li&gt;
                &lt;/ul&gt;
                
              &lt;/div&gt;
            &lt;/nav&gt;
      
            &lt;div class="header-banner row justify-content-center align-items-center blue-b"&gt;
              
              &lt;div class="col-12 red-b"&gt;
                &lt;h1&gt;YOUR FAVORITE SOURCE OF FREE BOOTSTRAP THEMES&lt;/h1&gt;
              &lt;/div&gt;
      
              &lt;div class="col-12 yellow-b"&gt;
                &lt;p class="header-paragraph text-center"&gt;lorem ipsum blablabla Montreal Canada&lt;/p&gt;
              &lt;/div&gt;
      
            &lt;/div&gt; &lt;!-- /.row --&gt;
            &lt;/div&gt;&lt;!-- /.container --&gt;
          &lt;/header&gt;
      
          &lt;!-- Optional JavaScript --&gt;
          &lt;!-- jQuery first, then Popper.js, then Bootstrap JS --&gt;
          &lt;script src="https://code.jquery.com/jquery-3.2.1.slim.min.js" integrity="sha384-KJ3o2DKtIkvYIK3UENzmM7KCkRr/rE9/Qpg6aAZGJwFDMVNA/GpGFF93hXpG5KkN" crossorigin="anonymous"&gt;&lt;/script&gt;
          &lt;script src="https://cdnjs.cloudflare.com/ajax/libs/popper.js/1.12.9/umd/popper.min.js" integrity="sha384-ApNbgh9B+Y1QKtv3Rn7W3mgPxhU9K/ScQsAP7hUibX39j7fakFPskvXusvfa0b4Q" crossorigin="anonymous"&gt;&lt;/script&gt;
          &lt;script src="https://maxcdn.bootstrapcdn.com/bootstrap/4.0.0/js/bootstrap.min.js" integrity="sha384-JZR6Spejh4U02d8jOt6vLEHfe/JQGiRRSQQxSfFWpi1MquVdAyjUar5+76PVCmYl" crossorigin="anonymous"&gt;&lt;/script&gt;
        &lt;/body&gt;
      &lt;/html&gt;</code></pre>
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