By default, most browsers set heads in bold. In this example, that means second-level heads (h2) and table heads (th). This differentiation seems unnecessary here, so I’ve chosen to set them back to normal.

  h2 {
    font-family: Georgia, serif;
+   font-weight: normal;
    text-align: center;
  }

And:

+ th {
+   font-weight: normal;
+ }

In my opinion, this gives the whole thing a more even look. Again, this is more a matter of personal preference than anything else.