Modal.php
protected function renderCloseButton()
    {
        if (($closeButton = $this->closeButton) !== false) {
            $tag = ArrayHelper::remove($closeButton, 'tag', 'button');
            $label = ArrayHelper::remove($closeButton, 'label', 'Close');
            if ($tag === 'button' && !isset($closeButton['type'])) {
                $closeButton['type'] = 'button';
            }

            return Html::tag($tag, $label, $closeButton);
        } else {
            return null;
        }
    }
protected function renderCloseButton()
    {
        if (($closeButton = $this->closeButton) !== false) {
            $tag = ArrayHelper::remove($closeButton, 'tag', 'button');
            $label = ArrayHelper::remove($closeButton, 'label', 'Close');
            if ($tag === 'button' && !isset($closeButton['type'])) {
                $closeButton['type'] = 'button';
            }

            return Html::tag($tag, $label, $closeButton);
        } else {
            return null;
        }
    }
Renders the close button.
@return string the rendering result