title: `justify-content` property not working on nested flexbox
body: <p>I'm quite new to HTML and CSS and I've encountered a problem with the menu I'm currently coding. </p>
  
  <p>I'd like to make a menu using nesting flexbox. It's getting close to what I want but for a reason I cannot understand, the <code>justify-content</code> inside the children flexbox doesn't seem to apply... </p>
  
  <p>Here is my 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>header {
    display: inline-flex;
    height: 90px;
    align-items: center;
    justify-content: flex-start;
  }
  .avatar {
    display: inline-flex;
    height: inherit;
    width: 200px;
    background-color: #00D717;
    align-items: center;
    justify-content: space-around;
  }
  .avatar h1 {
    font-size: 13px;
    text-transform: uppercase;
    color: white;
  }
  .resteHeader {
    display: inline-flex;
    height: inherit;
    justify-content: flex-start;
    align-items: center;
  }
  .resteHeader nav {
    display: inline-flex;
    height: inherit;
    justify-content: space-around;
    align-items: center;
  }
  .resteHeader nav ul {
    display: inline-flex;
    height: inherit;
    justify-content: space-between;
    align-items: center;
  }</code></pre>
  <pre class="snippet-code-html lang-html prettyprint-override"><code>&lt;header&gt;
    &lt;div class="avatar"&gt;
      &lt;img src="img/avatar.png"&gt;
      &lt;h1&gt;Hoang Nguyen&lt;/h1&gt;
    &lt;/div&gt;
    &lt;div class="resteHeader"&gt;
      &lt;nav&gt;
        &lt;ul&gt;
          &lt;li&gt;
            &lt;a href="#"&gt;
              &lt;img src="img/silhouette.png" alt=""&gt;
            &lt;/a&gt;
          &lt;/li&gt;
          &lt;li&gt;
            &lt;a href="#"&gt;
              &lt;img src="img/bulle.png" alt=""&gt;
            &lt;/a&gt;
          &lt;/li&gt;
          &lt;li&gt;
            &lt;a href="#"&gt;
              &lt;img src="img/cloche.png" alt=""&gt;
            &lt;/a&gt;
          &lt;/li&gt;
        &lt;/ul&gt;
      &lt;/nav&gt;
      &lt;img class="logo" src="img/logo.png" alt=""&gt;
      &lt;form&gt;
        Type sor search
        &lt;input type="text"&gt;
        &lt;img src="img/loupe.png" alt=""&gt;
      &lt;/form&gt;
    &lt;/div&gt;
  &lt;/header&gt;</code></pre>
  </div>
  </div>
  </p>
  
  <p>Thanks for your help ! </p>