Exemple de code de la propriété CSS border-collapse.

<style>
.border-collapse{ border-collapse : collapse; }
</style>
Tableau normal cellspacing="0" border="4" :
<table width="150" border="4" cellpadding="0" cellspacing="0">
 <tr> 
   <td> 1 </td>
   <td> 2 </td> 
 </tr>
 <tr> 
   <td> 3 </td>
   <td> 4 </td> 
 </tr>
</table>
Tableau normal cellspacing="0" border="4" :<br>
table{ border-collapse : collapse }
<table width="150" border="4" cellpadding="0" cellspacing="0" class="border-collapse">
 <tr> 
   <td> 1 </td>
   <td> 2 </td>
 </tr>
 <tr> 
   <td> 3 </td>
   <td> 4 </td>
 </tr>
</table>
Tableau normal cellspacing="3" border="4" :
<table width="150" border="4" cellpadding="0" cellspacing="3">
  <tr> 
   <td> 1 </td>
   <td> 2 </td>
 </tr>
 <tr> 
   <td> 3 </td>
   <td> 4 </td>
 </tr>
</table>
Tableau normal cellspacing="3" border="4" :<br>
table{ border-collapse : collapse }
<table width="150" border="4" cellpadding="0" cellspacing="3" class="border-collapse">
  <tr> 
   <td> 1 </td>
   <td> 2 </td>
 </tr>
 <tr> 
   <td> 3 </td>
   <td> 4 </td>
 </tr>
</table>
Tableau avec conflit :<br />
<style>
#bordercollapsea {
  border-collapse : collapse; 
  border : 5px solid yellow; 
}
#bordercollapsea *#col1 {
  border : 3px solid black; 
}
#bordercollapsea td { 
  border : 1px solid red; padding: 1em; 
}
#bordercollapsea td.solid-green{ 
  border : 5px solid green; 
}
#bordercollapsea td.solid-blue{ 
  border : 5px dashed blue; 
}
#bordercollapsea td.solid-red{ 
  border : 5px ridge red; 
}
</style>
<table id="bordercollapsea">
<col id="col1">
<col id="col2">
<col id="col3">
<tr id="row1">
    <td> 1 </td>
    <td> 2 </td>
    <td> 3 </td>
</tr>
<tr id="row2">
    <td> 4  </td>
    <td class="solid-blue"> 5 </td>
    <td class="solid-green"> 6 </td>
</tr>
<tr id="row3">
    <td> 7 </td>
    <td class="solid-red"> 8 </td>
    <td class="solid-green"> 9 </td>
</tr>
<tr id="row4">
    <td> 10 </td>
    <td> 11 </td>
    <td> 12 </td>
</tr>
<tr id="row5">
    <td> 13 </td>
    <td> 14 </td>
    <td> 15 </td>
</tr>
</table>