Drupal Menu Attributes

template.php

<?php


/**
 * Implements theme_menu_tree__[MENU NAME].
 */
function [THEME NAME]_menu_tree__[MENU NAME]($variables) {
  global $level;
  $class = ($level == 1) ? 'topnav' : 'subnav';
  return '<ul class="' . $class . '">' . $variables['tree'] . '</ul>';
}

/**
 * Implements theme_menu_link__[MENU NAME].
 */
function [THEME NAME]_menu_link__[MENU NAME]($variables) {

  unset($variables['element']['#attributes']['class']);
  $element = $variables['element'];
  $sub_menu = '';

  // set the global variable in order to use it in hook_menu_tree()
  // Named "level" to avoid confusing with $depth
  global $level;

  if ($element['#below']) {
    $sub_menu = drupal_render($element['#below']);
    $level = 1; // set the level as first for each list with submenu
    $element['#attributes']['class'][] = 'topnav__item';
  }

  else {
    $level = $element['#original_link']['depth'];
    $element['#attributes']['class'][] = 'subnav__item';
  }

  $output = l($element['#title'], $element['#href'], $element['#localized_options']);

  if(strpos($output, "active")>0){
    $element['#attributes']['class'][] = "current";
  }

  return '<li' . drupal_attributes($element['#attributes']) . '>' . $output . $sub_menu . "</li>\n";
}

?>

Customize the ul and li class of a Drupal submenu

This gets asked all over the place and I've come across lots of bullshit answers. This actually works. I didn't make this from scratch. I just customized the correct answers to match my needs.

Here's some sources:

http://drupal.stackexchange.com/questions/78171/assigning-custom-class-to-nested-menu-ul-elements
http://drupal.stackexchange.com/questions/10574/remove-classes-from-menu

Oh and don't add a third level menu. Just don't.