Improved CSS for Mediawiki Tables, assumes the daddio theme is installed and you've edited skins/Daddio.php and added the snippet below

skins_Daddio.php

<?php $this->text('stylepath') ?>/<?php $this->text('stylename') ?>/tables.css?<?php echo $GLOBALS['wgStyleVersion'] ?>";

tables.css

table
{ text-align: center;
font-family: Verdana;
font-weight: normal;
font-size: 11px;
color: #404040;
padding: 10px;
background-color: #BEC8D1;
border: 1px #6699CC solid;
border-collapse: collapse;
border-spacing: 0px; }

td.helpHed
{ border-bottom: 2px solid #6699CC;
border-left: 1px solid #6699CC;
background-color: #BEC8D1;
text-align: left;
text-indent: 5px;
font-family: Verdana;
font-weight: bold;
font-size: 11px;
padding-left: 20px;
padding-right: 20px;
color: #404040; }

td
{ border-bottom: 1px solid #9CF;
border-top: 0px;
border-left: 1px solid #9CF;
border-right: 0px;
text-align: left;
padding-left: 20px;
padding-right: 20px;
font-family: Verdana, sans-serif, Arial;
font-weight: normal;
font-size: 11px;
color: #404040;
background-color: #fafafa; }