<!DOCTYPE html>
<html>
<body>
<table id="myTable" border="1">
<tr>
<th>Month</th>
<th>Savings</th>
</tr>
<tr>
<td>January</td>
<td>$100</td>
</tr>
<tr>
<td>February</td>
<td>$150</td>
</tr>
</table>
<br>
<button type="button" onclick="myFunction()">Collapse border</button>
<script>
function myFunction() {
document.getElementById("myTable").style.borderCollapse = "collapse";
}
</script>
</body>
</html>