Theming forms in Drupal 7

I provide how to theme Drupal 7 Forms. in this example is Drupal Commerce Checkout Form

—-
  template.php
—-

/**
 * Implementation of hook_theme
 * Define themes to make style
 */
function yourtheme_theme($existing, $type, $theme, $path) {
  $base = array(
    'arguments' => array('form' => NULL),
    'render element' => 'form',
    'path' => drupal_get_path('theme', 'yourtheme') . '/templates/forms',
  );
 
  return array(
    'commerce_checkout_form_checkout' => $base + array(
      'template' => 'commerce-checkout-form-checkout',
    ),
  );
}
 
/**
 * Preprocessor for commerce_checkout_form_checkout theme
 */
function yourtheme_preprocess_commerce_checkout_form_checkout(&$variables) {
  /* Stuff with your variables */
}

—-
[yourtheme]/templates/forms/commerce-checkout-form-checkout.tpl.php
—-

<?php
  // stuff with $form
?>
Override