Drupal: Adding classes to blocks

block.tpl.php

<div id="<?php print $block_html_id; ?>" class="<?php print $classes; ?>"<?php print $attributes; ?>>

  <?php print render($title_prefix); ?>
  <?php if ($block->subject): ?>
    <h2<?php print $title_attributes; ?>><?php print $block->subject ?></h2>
  <?php endif;?>
  <?php print render($title_suffix); ?>

  <div <?php print $content_attributes; ?>>
    <?php print $content ?>
  </div>
</div>

hook_preprocess_block.php

<?php

/**
 * Implements hook_preprocess_block()
 */

function mytheme_preprocess_block(&$vars) {
  /* Set shortcut variables. Hooray for less typing! */
  $block_id = $vars['block']->module . '-' . $vars['block']->delta;
  $classes = &$vars['classes_array'];
  $title_classes = &$vars['title_attributes_array']['class'];
  $content_classes = &$vars['content_attributes_array']['class'];

  /* Add global classes to all blocks */
  $title_classes[] = 'block-title';
  $content_classes[] = 'block-content';

  #print $block_id . '<br/>';

  /* Add classes based on the block delta. */
  switch ($block_id) {
    /* System Navigation block */
    case 'system-navigation':
      $classes[] = 'block-rounded';
      $title_classes[] = 'block-fancy-title';
      $content_classes[] = 'block-fancy-content';
      break;
    /* Main Menu block */
    case 'system-main-menu':
    /* User Login block */
    case 'user-login':
      $title_classes[] = 'element-invisible';
      break;
  }
}