Block themes are built for the newer functionality in WordPress and allow you to use blocks to edit all parts of your site, including easier ways to quickly customize everything from your background colours to font sizes for all Heading blocks etc.
Comparatively, classic themes are built with PHP templates, functions.php and more that include features like Widgets, a dedicated Menus section, the Customizer, and more.
| Capability | Site themes | Classic themes |
|---|---|---|
| Block editor – Edit content | Yes | Yes |
| Site editor – Full Site Editing | Yes | No |
| Navigation menus | Editor > Navigation | Appearance > Menus |
| Widgets | Use blocks | Appearance > Widgets |
| Customiser | Site editor > Styles | Appearance > Customise |
| theme.json | Yes | Optional |
| style.css | Yes – but mostly empty | Yes |
| templates and parts | In database and/or HTML | PHP |
| patterns | In database and/or PHP | In database and/or PHP |
| font library | Yes | ? |
Classic themes do not work with the Site Editor.
Hybrid and Universal themes are somewhere between a classic and block theme.
See Bridging the gap: Hybrid themes