src/Widgets/Bootstrap/Card.php
protected function renderOverlayImage() {
        if (!isset($this->overlayImage)) {
            return '';
        }
        Html::addCssClass($this->footerImageOptions, ['widget' => 'card-img-bottom']);
        return $this->htmlHlp->img($this->overlayImage, ['class' => 'card-img']);
    }
protected function renderOverlayImage() {
        if (!isset($this->overlayImage)) {
            return '';
        }
        Html::addCssClass($this->footerImageOptions, ['widget' => 'card-img-bottom']);
        return $this->htmlHlp->img($this->overlayImage, ['class' => 'card-img']);
    }
Render card bottom image
@return string