gistfile1.phtml

<?php
// Variable for keeping track if a user has posted.  Set to false initially.  If found it will be changed to true.
$alreadyPosted = false;
// Loop through all the posts
foreach ($posts_array as $post) {
 // Check to see if the person in the database ($post['name']) matches the supplied name ($name)
  if ($post['name'] == $name) {
    // It does.  Great.  Set the variable to true.
    $alreadyPosted = true;
    break;
  }
}?>

<div
<?php
  if ($alreadyPosted) {
    echo 'id="highlight"';
  }
?>