title: HTML/CSS @media Query : The line keeps disappearing
body: <p>I couldn't understand the part of studying CSS.
  If I decrease the browser size, the line disappears. 
  I don't know why. 
  Can't I keep the line from disappearing?
  I have no idea why it's disappearing.
  Please help me.</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>.container {
    position:relative;
    border: solid 1px black;
  }
  
  @media screen and (min-width:600px) {
   nav {
    float: left;
    width: 25%;
    border: solid 1px skyblue;
  }
  
  section {
    margin-left:25%;
    border: solid 1px orange;
  } 
  }
  
  @media screen and (max-width: 599px) {
    nav li {
      display: inline;
    }
  }</code></pre>
  <pre class="snippet-code-html lang-html prettyprint-override"><code>&lt;!DOCTYPE html&gt;
  &lt;html&gt;
  
  &lt;head&gt;
    &lt;meta charset="utf-8"&gt;
    &lt;meta name="viewport" content="width=device-width"&gt;
    &lt;title&gt;JS Bin&lt;/title&gt;
  &lt;/head&gt;
  
  &lt;body&gt;
    &lt;div class="container"&gt;
      &lt;nav&gt;
        &lt;ul&gt;
          &lt;li&gt;Home&lt;/li&gt;
          &lt;li&gt;Taco Menu&lt;/li&gt;
          &lt;li&gt;Draft List&lt;/li&gt;
          &lt;li&gt;Hours&lt;/li&gt;
        &lt;/ul&gt;
      &lt;/nav&gt;
      &lt;section&gt;
        &lt;p&gt;Lorem ipsum dolor sit amet, consectetur adipisicing elit. Vero odit, dolorem dolore, porro repudiandae animi iusto, quia quae autem voluptate minus ducimus cupiditate ipsum! Fugit assumenda error veritatis pariatur expedita.&lt;/p&gt;
      &lt;/section&gt;
      &lt;section&gt;
        &lt;p&gt;Lorem ipsum dolor sit amet, consectetur adipisicing elit. Ad fugiat, nulla officiis quibusdam iusto non. Sint suscipit pariatur aspernatur amet iusto aperiam est nesciunt ullam. Labore sit, ut ipsum neque.&lt;/p&gt;
      &lt;/section&gt;
    &lt;/div&gt;
  &lt;/body&gt;
  
  &lt;/html&gt;</code></pre>
  </div>
  </div>
  </p>