The function is defined as menu callback from the following code:
`$items['admin/appearance/settings'] = array(`
` 'title' => 'Settings',`
` 'description' => 'Configure default and theme specific settings.',`
` 'page callback' => 'drupal_get_form',`
` 'page arguments' => array('system_theme_settings'),`
` 'access arguments' => array('administer themes'),`
` 'type' => MENU_LOCAL_TASK,`
` 'file' => 'system.admin.inc',`
` 'weight' => 20,`
`);`