Try it Editor: Border-collapse

Edit This Code :

<!DOCTYPE html>
<html>
<head>
<style>
table, td, th {
    border: 1px solid black;
}

#table1 {
    border-collapse: separate;
}

#table2 {
    border-collapse: collapse;
}
</style>
</head>
<body>

<h2>border-collapse: separate (default):</h2>
<table id="table1">
  <tr>
    <th>Firstname</th>
    <th>Lastname</th>
  </tr>
  <tr>
    <td>Peter</td>
    <td>Griffin</td>
  </tr>
  <tr>
    <td>Lois</td>
    <td>Griffin</td>
  </tr>
</table>

<h2>border-collapse: collapse:</h2>
<table id="table2">
  <tr>
    <th>Firstname</th>
    <th>Lastname</th>
  </tr>
  <tr>
    <td>Peter</td>
    <td>Griffin</td>
  </tr>
  <tr>
    <td>Lois</td>
    <td>Griffin</td>
  </tr>
</table>

</body>
</html>
Result :