Being new to d3.js, I am trying to write a simple code to compute font-sizes for paragraphs from an array. This is my code:

```
<html>
<head>
<script src="http://d3js.org/d3.v3.min.js" charset="utf-8"></script>
<script>
    d3.select('body')
      .selectAll('p')
      .data([5,10])
      .style("font-size", function(d) { return d + "px"; });
</script>
</head>
<body>
<p>para 1</p>
<p>para 2</p>
</body>
</html>

```

It seems like a very simple thing to do but for some reason isn't working. Any help as to where I am going wrong would really help.