title: Why <ul> adds extra top margin?
body: <p>I have a simple html page with some style in it and I do not understand why the  adds some top margin?</p>
  
  <p>Here is the source:</p>
  
  <p><div class="snippet" data-lang="js" data-hide="false" data-console="false" data-babel="false">
  <div class="snippet-code">
  <pre class="snippet-code-html lang-html prettyprint-override"><code>&lt;!doctype html&gt;
  &lt;html&gt;
  
  &lt;head&gt;
    &lt;title&gt;&lt;/title&gt;
    &lt;style type="text/css"&gt;
      body {
        margin: 0;
        padding: 0;
        background-color: #ffffcc;
      }
      #content {
        width: 900px;
        margin-left: auto;
        margin-right: auto;
        border: 0;
        background-color: #ccccff;
      }
    &lt;/style&gt;
  &lt;/head&gt;
  
  &lt;body&gt;
    &lt;div id="content"&gt;
      &lt;div&gt;
        &lt;ul&gt;
          &lt;li&gt;&lt;a href="./xxx.html"&gt;xxx&lt;/a&gt;
          &lt;/li&gt;
          &lt;li&gt;&lt;a href="./yyy.html"&gt;yyy&lt;/a&gt;
          &lt;/li&gt;
          &lt;li&gt;&lt;a href="./zzzz.html"&gt;zzz&lt;/a&gt;
          &lt;/li&gt;
        &lt;/ul&gt;
      &lt;/div&gt;
    &lt;/div&gt;
  &lt;/body&gt;
  
  &lt;/html&gt;</code></pre>
  </div>
  </div>
  </p>
  
  <p>Here is the "annoying" space.</p>
  
  <p><img src="https://i.stack.imgur.com/LMHh1.jpg" alt="enter image description here"></p>
  
  <p>If I add "margin-top : 0;"  to the  the space is gone...but I I'm not happy until I understand why. </p>