public function addCustomBodyClass(string $class, string $element, bool $first = false) : Bootstrap4Card
    {
        if (in_array($element, $this->body_elements) === true) {
            $this->body_classes[$element][] = $class;

            if ($first === true) {
                $this->body_classes_first[$element][$class] = true;
            }
        }

        return $this;
    }