Here's the DOCTYPE:

!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Strict//EN"
        "http://www.w3.org/TR/xhtml1/DTD/xhtml1-strict.dtd"

Here's the CSS:

body {font: 0.8em black Verdana, Arial, sans-serif;}
table {border: 1px solid black; width: 300px; margin: 50px;}
th {font-weight: 800; border-bottom: 1px solid black; border-right: 1px solid black;}
td {padding: 5px; color: black; border-right: 1px solid blue; border-bottom: 1px solid blue; text-align: center;}
td:empty {background-color: yellow; border: 1px dashed red; margin: 1px;}