title: How can I remove space (margin) above HTML header?
body: <p>I am creating a website.</p>
  
  <p>I have written the HTML part and now I am writing the stylesheet. But there is always some space above my header. How can I remove it?</p>
  
  <p>My HTML and CSS code is given below.</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>body{
    margin: 0px;
    padding: 0px;
  }
  
  header{
    margin: 0px;
    padding: 0px;
    height: 20em;
    background-color: #C0C0C0;
  }</code></pre>
  <pre class="snippet-code-html lang-html prettyprint-override"><code>&lt;header&gt;
    &lt;h1&gt;OQ Online Judge&lt;/h1&gt;
    &lt;form action="&lt;?php echo base_url();?&gt;/index.php/base/si" method="post"&gt;
      &lt;label for="email1"&gt;E-mail : &lt;/label&gt;&lt;input type="text" name="email" id="email1"&gt;
      &lt;label for="password1"&gt;Password : &lt;/label&gt;&lt;input type="password" name="password" id="password1"&gt;
      &lt;input type="submit" name="submit" value="Login"&gt;
    &lt;/form&gt;
  &lt;/header&gt;</code></pre>
  </div>
  </div>
  </p>