Add classes to login form fields D 7
You can do this by altering the form in your custom module hook_form_alter(){} or 
in template.php of your active theme.

Just add the classes in the attributes array().

Or you can create a user-login.tpl.php file following this link, Its already answered here with this code. 

&lt;?php
    function operationscheck_theme_theme() {
    $items = array();
    $items['user_login'] = array(
   'render element' =&gt; 'form',
   'path' =&gt; drupal_get_path('theme', 'operationscheck_theme') . '/templates',
   'template' =&gt; 'user-login',

    'preprocess functions' =&gt; array(
   'operationscheck_theme_preprocess_user_login'
   ),
);
    $items['user_pass'] = array(
   'render element' =&gt; 'form',
   'path' =&gt; drupal_get_path('theme', 'operationscheck_theme') . '/templates',
   'template' =&gt; 'user-pass',
   'preprocess functions' =&gt; array(
   'operationscheck_theme_preprocess_user_pass'
  ),
);
 $items['user_register_form'] = array(
'render element' =&gt; 'form',
'path' =&gt; drupal_get_path('theme', 'operationscheck_theme') . '/templates',
'template' =&gt; 'user-register-form',
'preprocess functions' =&gt; array(
'operationscheck_theme_preprocess_user_register_form'
 ),
);

return $items;
}
?&gt;

&lt;?php
   function operationscheck_theme_preprocess_user_login(&amp;$vars) {
      $vars['intro_text'] = t('This is my awesome login form');
    }
   function operationscheck_theme_preprocess_user_login(&amp;$vars) {
     $vars['intro_text'] = t('This is my awesome pass form');
   }

function operationscheck_theme_preprocess_user_register_form(&amp;$vars) {
    $vars['intro_text'] = t('This is my super awesome reg form');
   }

 function operationscheck_theme_theme(&amp;$existing, $type, $theme, $path) {
  $hooks = operationscheck_theme_theme($existing, $type, $theme, $path)

  $hooks['user_login_block'] = array(
 'template' =&gt; 'user-login',
 'arguments' =&gt; array('form' =&gt; NULL)
 );

// @TODO: Needs detailed comments. Patches welcome!
return $hooks;

}

function operationscheck_theme_preprocess_user_login_block(&amp;$variables) {
  $variables['intro_text'] = t('This is my awesome login formX');
  $variables['rendered'] = drupal_render($variables['form']);
}
 ?&gt;


Please check if it is the code snippet you were looking for.