Hi,
You can add the above code under the body tag. You need to copy the header.php file from the parent theme folder(can be found here > wp-content/themes/kleo/) to child theme folder(this folder> wp-content/themes/kleo-child/). then you can edit header.php and place your code below <body> tag. however, You can integrate facebook login to your website without using the above code just by going to Theme Options>Miscellaneous>Facebook integration and turn it on and set your Facebook APP ID in the box. Then you can let user login via facebook. I have attached a screenshot for better understanding. I hope this help. Thanks,
Kamal
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