Where / How to edit styles ( CSS ) ?

Main Theme’s – style.css Customizer’s
Additional CSS panel
Child Theme’s
style.css
Child Theme’s custom.css
Location: child theme folder / custom.css
X Ok Ok Ok
DO NOT edit style.css of main theme itself.
This will create issue while theme update.
If you have minor style changes you may use this.

Keep back up of those styles, in case of accidental reset.

You can place custom styles in style.css of child theme

It cannot override styles from responsive.css, customizer etc.

This is useful if you need to override styles from responsive.css, customizer or any other css including style.css of main theme.
So better to prefer this.