pokk,
<!DOCTYPE html>
<html>
<head>
<title>Untitled</title>
<meta charset="utf-8">
<style type="text/css">
.demo td:nth-child(1){
width :198px;
background-color: #FF00FF;
}
.demo td:nth-child(2){
width :545px;
background-color: #0000FF;
}
.demo td:nth-child(2) input{
width :80px;
background-color: #FFFF00;
}
</style>
</head>
<body>
<table id="center_tabl" class="demo">
<tr>
<th colspan="2" id="id_sernumber_clik" class="tabl" name="N_SerNumber" id="TablCondSerNumber">Заголовок</th>
</tr>
<!------------------------------------------------------------------ -->
<tr>
<td id="table_left">Включить/Выключить</td>
<td colspan="2" id="table_right">
<input id="id_ButOn" name="N_ButOn" type="button" value="Включить">
<input id="id_ButOff" name="N_ButOff" type="button" value="Выключить">
</td>
</tr>
<!------------------------------------------------------------------ -->
</table>
</body>
</html>