css3 flex, flex container, html5

<!DOCTYPE html>
<html>

  <head>
    <link rel="stylesheet" href="style.css">
    <script src="script.js"></script>
  </head>

  <style>
    .my-flex-container {
      display: flex;
      width: 400px;
      height: 300px;
      flex-direction: row;
    }
    
    .my-left-nav {
      flex: 0;
      background-color: green;
    }
    
    .my-main-item {
      flex: 1;
      background-color: pink;
    }
    
    .my-right-nav {
      flex: 0;
      background-color: yellow;
    }
  </style>
  <body>
    <div class="my-flex-container">
      <div class="my-left-nav">
        <div style="width:80px;">
          
        </div>
      </div>
      <div class="my-main-item">
        
      </div>
      <div class="my-right-nav">
        <div style="transform:rotate(90deg);margin-top:100px;">
          <pre>Right Nav</pre>
        </div>
      </div>
    </div>
  </body>

</html>

// Code goes here

/* Styles go here */