If you’re making heavy modifications to the core theme then yes, we’d recommend doing so. You can download a child theme for Shoptimizer here.
This child theme will work with any version of Shoptimizer. You don’t need to update it if the parent theme is updated!
Small CSS tweaks
If however, you’re making just small CSS adjustments, these can go into Appearance > Customize > Additional CSS.
Shoptimizer - find out more
The fast WooCommerce theme built for speed and conversions.