add css and js in preprocess page

template.php

<?php

/**
 * Preprocess page.
 */
function mytheme_preprocess_page(&$vars) {

  drupal_add_css(path_to_theme() . '/css/foo.css', 'theme', 'all');
  $vars['styles'] = drupal_get_css();

  drupal_add_js(path_to_theme() . '/js/foo.js');
  $vars['scripts'] = drupal_get_js();

}