Description: Selects even elements, zero-indexed. See also odd.
In particular, note that the 0-based indexing means that, counter-intuitively, :even selects the first element, third element, and so on within the matched set.
<!DOCTYPE html>
<html>
<head>
  <style>
  table {
    background:#eeeeee;
  }
  </style>
  <script src="https://code.jquery.com/jquery-latest.js"></script>
</head>
<body>
	<table border="1">
    <tr><td>Row with Index #0</td></tr>
    <tr><td>Row with Index #1</td></tr>
    <tr><td>Row with Index #2</td></tr>
    <tr><td>Row with Index #3</td></tr>
  </table>
<script>$("tr:even").css("background-color", "#bbbbff");</script>
</body>
</html>