<div class="principal">
   <h2>Properties for the flex container</h2>
   <div class="control">
      <h4><a href="http://w3.unpocodetodo.info/css3/flex-direction.php">flex-direction</a> <small>( property of the flex container  )</small></h4>
      <!--flex-direction: row | row-reverse | column | column-reverse;-->
      <div class="radio">
         <input name="flex-direction" type="radio"  class="flex-direction" id="R11" value="row" checked><label for="R11">row:</label>
         <input name="flex-direction