How do I count how many top level categories there are?

I need to calculate some dynamic CSS based on how many top level categories exist. (NOT how many posts are in a category, or how many categories a post belongs to… Nothing about posts at all, just how many top level categories there are)

I am new to PHP, but I couldn’t find any WP functions that would return the number I’m looking for.

Thanks in advance for any help.

As the Codex says, this is the code block to query for only the Top Label categories — the parents. With this, I used the PHP function count().

<?php    
$args = array(
  'parent' => 0,
  'hide_empty' => 0
  );

$categories = get_categories( $args );

echo count( $categories );    
?>