What does 'critical hits' apply to?

https://preview.redd.it/odl5eh077bie1.png?width=925&format=png&auto=webp&s=8482ea2f0b77fdf832d9faf932804750019891ba

https://preview.redd.it/upfufi077bie1.png?width=259&format=png&auto=webp&s=356280d4264cf7f242c4533b9dffd30e138e0c31

Karlach landed a critical hit with this bow. I'm confused about the extra damage - does the critical hit dice roll only apply to the main piercing damage, or does it apply to all the 'extra' bits of damage (the cold, acid, fire)? Thank you.