One of Shopify’s key strengths is the in-depth documentation and help scripts which are out there as a free resource.
I recently had a need to build in some colour and sizing chart popups to a site’s product pages (Minimal theme). Sure enough that need was satisfied by some excellent documentation which I adapted to suit the purpose.
Basically it involved creating dedicated pages for the chart contents and then editing some of the theme pages to make the popups work by referencing variations and linking those to qualify for a theme button on a product page which instigated the appropriate colour or size popup chart.
See it in action at West Coast Ganseys