Cake\View\Helper\FormHelper::day PHP Method

    public function day($fieldName = null, array $options = [])
    {
        $options = $this->_singleDatetime($options, 'day');
        if (isset($options['val']) && $options['val'] > 0 && $options['val'] <= 31) {
            $options['val'] = ['year' => date('Y'), 'month' => date('m'), 'day' => (int) $options['val']];
        }
        return $this->dateTime($fieldName, $options);
    }

 public function day($fieldName = null, array $options = [])
 {
     $options = $this->_injectStyles($options, 'form-control');
     return parent::day($fieldName, $options);
 }