You can place PHP snippets at the bottom of your child theme functions.php file (before "?>" if you have it). CSS, on the other hand, goes in your child theme style.css file. Make sure you know what you are doing when editing such delicate files - if you need more guidance, please take a look at my free WooCommerce Customization video tutorial.
Does this snippet still work?
Please let me know in the comments if everything worked as expected. I would be happy to revise the snippet if you report otherwise (please provide screenshots). I have tested this code with Storefront theme, the WooCommerce version listed above and a WordPress-friendly hosting on PHP 7.
If you think this code saved you time & money, please join other Business Bloomer supporters and avail of 365 days of WooCommerce benefits. Thank you in advance :)
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Author, WooCommerce expert, WordCamp speaker and Internet marketer, Rodolfo Melogli has worked as a WooCommerce freelancer since 2011. He helps entrepreneurs and developers overcome their WooCommerce nightmares :) Rodolfo is the organiser of WordCamp Dublin, the Dublin WooCommerce Meetup, the Dublin Ecommerce Meetup and the Dublin WordPress Meetup. He enjoys interacting with people, travelling and chasing tennis & soccer balls. Of course, he loves pizza too.