Block Theme Global Styles

Use theme.json as structured design data, not as a place to paste arbitrary CSS. WordPress merges core defaults, theme data, child-theme data, user Global Styles, and block-level styles; verify both editor and front-end output after every structural change.

Start with the supported schema

WordPress 7.1 still uses theme.json schema version 3:

{
  "$schema": "https://schemas.wp.org/trunk/theme.json",
  "version": 3,
  "settings": {},
  "styles": {}
}

Use the trunk schema while developing against the current WordPress release, and validate the file as JSON. The schema version and WordPress release number are separate concepts; do not write "version": 7.1.