HTML table nth(even) background-color

<!DOCTYPE html>
<html>
<head>
<style>
table {
    border-collapse: collapse;
    width: 100%;
}

th, td {
    text-align: left;
    padding: 8px;
}

tr:nth-child(even){
    background-color: #f2f2f2
}

th {
    background-color: blue;
    color: white;
}
</style>
</head>
<body>

<h2>Colored Table Header</h2>

<table>
  <tr>
    <th>Firstname</th>
    <th>Lastname</th>
    <th>Savings</th>
  </tr>
  <tr>
    <td>Peter</td>
    <td>Griffin</td>
    <td>$100</td>
  </tr>
  <tr>
    <td>Lois</td>
    <td>Griffin</td>
    <td>$150</td>
  </tr>
  <tr>
    <td>Joe</td>
    <td>Swanson</td>
    <td>$300</td>
  </tr>
  <tr>
    <td>Cleveland</td>
    <td>Brown</td>
    <td>$250</td>
</tr>
</table>

</body>
</html>