[Preprocess html samples] From https://github.com/Krimson/wundertheme/blob/master/template.php #d7

template.php

/**
 * Override or insert variables into the html template.
 *
 * @param $variables
 *   An array of variables to pass to the theme template.
 * @param $hook
 *   The name of the template being rendered. This is usually "html", but can
 *   also be "maintenance_page" since zen_preprocess_maintenance_page() calls
 *   this function to have consistent variables.
 */
function MY_THEME_preprocess_html(&$variables, $hook) {

  $theme_path = drupal_get_path('theme', 'wundertheme');

  drupal_add_css( $theme_path . '/stylesheets/ie.css',
    array(
      'group' => CSS_THEME,
      'browsers' => array(
        'IE' => 'lt IE 9',
        '!IE' => FALSE,
      ),
      'weight' => 999,
      'every_page' => TRUE,
      'media' => 'screen, projection'
    )
  );
  drupal_add_css( $theme_path . '/stylesheets/style.css',
    array(
      'group' => CSS_THEME,
      'browsers' => array(
        'IE' => 'gt IE 8',
        '!IE' => TRUE,
      ),
      'weight' => 999,
      'every_page' => TRUE,
      'media' => 'screen, projection'
    )
  );
  drupal_add_css( $theme_path . '/stylesheets/print.css',
    array(
      'group' => CSS_THEME,
      'weight' => 999,
      'every_page' => TRUE,
      'media' => 'print'
    )
  );
  $variables['favicon'] = url($theme_path . '/favicon.ico');
}