1.) Create di.xml in at etc\frontend
Using plugin we can add body class at any page.
type="Vendor\Module\Plugin\Result\Page"
2.) In page.php file
namespace Vendor\Module\Plugin\Result;
use Magento\Framework\App\ResponseInterface;
class Page
{
private $context;
public function __construct(
\Magento\Framework\View\Element\Context $context
) {
$this->context = $context;
}
public function beforeRenderResult(
\Magento\Framework\View\Result\Page $subject,
ResponseInterface $response
){
if(condition) {
if($this->context->getRequest()->getFullActionName() == 'checkout_onepage_success') {
$subject->getConfig()->addBodyClass('advance-success-page');
}
}
return [$response];
}
}