Только из-за того, что ваш оригинальный код сделал мне больно:
<style type="text/css">
.mainTable { border-collapse: collapse; font-family: Tahoma, sans-serif; margin: 0 auto; width: 80%; }
.mainTable td, .mainTable th { padding: 3px; }
.mainTable .branding { color: #999999; }
.mainTable .header { background-color: #6DA2D7; color: #FFFFFF; }
.mainTable .small { font-size: small; }
.mainTable .x-large { font-size: x-large; }
.mainTable .left { text-align: left; }
.mainTable .right { text-align: right; }
.mainTable .center { text-align: center; }
.mainTable .odd { background-color: #FFFFFF; }
.mainTable .even { background-color: #EEEEEE; }
.subTable { border: 1px solid #000000; border-collapse: collapse; margin: 0 auto; width: 90%; }
.subTable td { border-bottom: 1px solid #000000; border-right: 1px dotted #000000; }
.subTable .header { background-color: #055770; border: 1px solid #000000; }
.subTable .subheader { background-color: #256B9C; border: 1px solid #000000; color: #FFFFFF; }
.subTable .high { color: #FF0000; font-weight: bold; }
.subTable .med { color: #FF9900; }
.subTable .low { color: #009900; }
</style>
<table class="mainTable">
<tr><td class="x-large" colspan="3"><span class="branding">XYZ|</span> ABC</td></tr>
<tr class="header"><td> </td><td class="small">Date</td><td class="right">Monitoring</td></tr>
<tr><td class="small">Tool hourly report</td><td colspan="2"> </td></tr>
<tr>
<td colspan="3">
<table class="subTable small center">
<tr class="header left"><th colspan="3">Disk Space</th></tr>
<tr class="subheader"><th>Machine</th><th>Status</th></tr>
<tr class="odd"><td>BN stpmus@sn2437</td><td class="high">85% full</td></tr>
<tr class="even"><td>GH stpma@sn2597</td><td class="med">51% full</td></tr>
<tr class="odd"><td>US1 stpmu1@sn2598</td><td class="low">1% full</td></tr>
<tr class="even"><td>US2 stpmu2@sn2499</td><td class="low">9% full</td></tr>
</table>
</td>
</tr>
</table>