title: Why I can't change the font size of last h3 only
body: <p>I'm making a web page containing multiple titles. I have a problem and that is I can't change the font size of h3 (last one) and if I did the whole font sizes of other titles changes too. I want to know why and how to solve this.</p>
  <p>This the 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-css lang-css prettyprint-override"><code>.join_us {
    width: 100%;
    margin-top: 50px;
  }
  
  .join_us h3 {
    font-size: 20px;
    font-family: 'sans-serif';
    font-weight: bold;
    text-align: center;
    color: #2D2D2D;
  }
  
  .join_us .create_account_container {
    width: 400px;
    height: 60px;
    margin-left: auto;
    margin-right: auto;
    background-color: #0EBA00;
    margin-top: 40px;
    text-align: center;
  }
  
  .join_us .create_account_container a {
    text-decoration: none;
    line-height: 60px;
    font-size: 25px;
    font-family: 'sans-serif';
    font-weight: bold;
    text-align: center;
    color: #FFF;
  }
  
  .invite_for_use_section h1 {
    font-size: 28px;
    font-family: 'sans-serif';
    color: #000;
    font-weight: bold;
    text-align: center;
    line-height: 40px;
    margin-top: 30px;
  }
  
  .invite_for_use_section h3 {
    font-size: 13px;
    font-family: 'sans-serif';
    font-weight: bold;
    text-align: center;
    color: #2D2D2D;
  }</code></pre>
  <pre class="snippet-code-html lang-html prettyprint-override"><code>&lt;div class="join_us"&gt;
    &lt;h3&gt;JOIN OVER 10,000 SMART AFFILIATE MARKETERS! GET STARTED NOW...&lt;/h3&gt;
    &lt;div class="create_account_container"&gt;
      &lt;a href=""&gt;CREATE MY ACCOUNT&lt;/a&gt;
    &lt;/div&gt;
  &lt;/div&gt;
  
  &lt;div class="invite_for_use_section"&gt;
    &lt;h1&gt;
      Use Our Secret Tool and Boost Your Commissions Up to 5X More While Cutting Your Workload To Shreds!
    &lt;/h1&gt;
    &lt;br&gt;
  
    &lt;h3&gt;
      Over 10,000 (and growing) People Can't Be Wrong!
    &lt;/h3&gt;
  &lt;/div&gt;</code></pre>
  </div>
  </div>
  </p>
  <p>The page also contain header which contain h1 titles didn't include it because I think it has no relation to this problem.</p>