Adding Bootstrap Forms to WooCommerce

gistfile1.php

add_filter('woocommerce_billing_fields', 'custom_woocommerce_billing_fields');

function custom_woocommerce_billing_fields( $fields ) {
  $fields['billing_address_1']['class'] = array( 'form-group' );
  $fields['billing_address_1']['input_class'] = array( 'form-control' );
  return $fields;
}

or

add_filter('woocommerce_form_field_args', 'wc_form_field_args',10,3); function wc_form_field_args($args, $key, $value) { $args['input_class'] = array( 'form-control' ); return $args; }