Where is the functions.php file in WordPress?

Hi, while trying to copy paste a code from some google page, I lost function.php entire code, Can you please help in backup?

Thanks for the great video. For some reason, I can't access the php files through the appearance tab. I had to go into the cpanel.

Of all the video tutorial regarding hook and modifying function.php, you're the only one showed me these steps. Thank you so much! :)

Hello and thank you for the video ...
I actually cannot find any codes in theme editor ... Would that be a new WP solution or something is wrong with my WP ...? I use to using this method to edit the codes, but this time I can see nothing, only some weird visual editor. No switcher for code editor as well.
Thank you.