Overriding breadcrumbs in Drupal 7

template.php

<?php
function my_awesome_theme_breadcrumb($variables) {
  $breadcrumb = $variables['breadcrumb'];
 
  if (!empty($breadcrumb)) {
    // Provide a navigational heading to give context for breadcrumb links to
    // screen-reader users. Make the heading invisible with .element-invisible.
    $output = '<h2 class="element-invisible">' . t('You are here') . '</h2>';
 
    // Add 'my-awesome-class' to the breadcrumb wrapper and change the separators from '»' to '::'.
    $output .= '<div class="breadcrumb my-awesome-class">' . implode(' :: ', $breadcrumb) . '</div>';
    return $output;
  }
}