I'm attempting to convert an element. The font-size conversion works fine, but the margin conversion isn't doing so great.

Here is my attempt:

```
<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">    
<html>
    <head>
    <style type="text/css">
    .box{
        font-size:30px;
        margin:23px 0;
        font-weight:bold;

    }
    </style>
    </head>

<body>

</head>
<body>

<div class="box">Some text here</div>

</body>
</html>

```

Compared to:

```
<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">    
<html>
    <head>
    <style type="text/css">
    body{
        font-size:20px;
    }
    </style>
    </head>

<body>

</head>
<body>

<h2>Some text here</h2>

</body>
</html>

```

As you can see, the H2 and the .box text have the same font-size when viewed in a browser.

This is incorrect, and should be 24px. What mistake have I made?