title: Margin 0 in header, nav
body: <p>Setting <code>margin: 0</code> doesn't in <code>header{}</code> or <code>nav{}</code> but works as expected in <code>ul{}</code>. I thought that <code>ul{margin:0}</code> would not not work since <code>header</code> and <code>nav</code> are parents.</p>
  
  <pre><code>&lt;head&gt;
      &lt;meta charset="UTF-8"&gt;
      &lt;title&gt;Compañía&lt;/title&gt;
      &lt;link rel="stylesheet" href="estilo.css"&gt; &lt;/head&gt;
  
  &lt;body&gt;
      &lt;header&gt;
          &lt;nav&gt;
              &lt;ul&gt;
                  &lt;li&gt;&lt;a href="#"&gt;About&lt;/a&gt;&lt;/li&gt;
                  &lt;li&gt;&lt;a href="#"&gt;Products&lt;/a&gt;&lt;/li&gt;
                  &lt;li&gt;&lt;a href="#"&gt;Purchase&lt;/a&gt;&lt;/li&gt;
                  &lt;li&gt;&lt;a href="#"&gt;Contact&lt;/a&gt;&lt;/li&gt;
              &lt;/ul&gt;
          &lt;/nav&gt;
      &lt;/header&gt;
  &lt;/body&gt;
  
  &lt;/html&gt;
  </code></pre>
  
  <hr>
  
  <pre><code>body {
      margin: 0;
      padding: 0;
  }
  
  header {
      background-color: darkseagreen;
      height: 420px;
      margin: 0;
      padding: 0;
  }
  
  nav {
      margin: 0;
  }
  </code></pre>
  
  <p><a href="https://i.stack.imgur.com/10dov.png" rel="nofollow noreferrer">Link to example image</a></p>