Tryit Editor v1.8

Source Code:
<!DOCTYPE html>
<html>
<head>
<style>
.box
{
display:-ms-flexbox;
display:-moz-box;
display:-webkit-box;
display:box;
width:200px;
height:100px;
border:2px solid red;
}
</style>
<script>
function ChangeBoxAlign(x)
{
// Returns the selected option's text
var boxAlign=x.options[x.selectedIndex].text;
var div=document.getElementById("myDiv");
if (div.style.MozBoxAlign!==undefined)
  {
  div.style.MozBoxAlign=boxAlign;
  }
else if (div.style.webkitBoxAlign!==undefined)
  {
  div.style.webkitBoxAlign=boxAlign;
  }
else if (div.style.msFlexAlign!==undefined)
  {
  div.style.msFlexAlign=boxAlign;
  }
else
  {
  alert("Your browser doesn't support this example!");
  }
}
</script>
</head>
<body>
<div class="box" id="myDiv">
  <b>first child</b>
  <i>second child</i>
</div>

<select onchange="ChangeBoxAlign (this);" size="6">
  <option selected="selected" />baseline
  <option />center
  <option />end
  <option />inherit
  <option />start
  <option />stretch
</select>

<p><b>Note:</b> This example does not work in Opera, or Internet Explorer 9 and earlier.</p>

</body>
</html>
Result:
W3Schools.com - Try it yourself