Theme development

• Theme contractWhat a theme is, the fields of theme.json, required files, package rules, template resolution order (@Theme) and partial overriding.
• Templates and Twig helpersThe skeleton and blocks of the main template, overriding module templates, safe helpers that do not start a session and a reference of all Twig functions/filters.
• Menu, widgets and appearanceMenu locations, widget areas and types, the brand colours and fonts the administrator chooses, cookie consent.
• CSS, JS and assetsThe theme's dist/ output, versioned delivery, copying of fonts and images referenced in CSS, your own build tool and how it differs from the core style build.
• Packaging and publishing a themePreparing the theme zip, the contract check, installing on your own site and for customers, the store and signed catalogue, compatibility and the theme development checklist.