Changeset 52675 for trunk/tests/phpunit/tests/theme/globalStylesheet.php

Fix: Classic themes using default presets are not working.

This commit makes the presets provided by the theme via add_theme_support always create CSS Custom Properties, whether or not the theme has a theme.json file. This way, if the overwrites a core preset, the core CSS variables are also overwritten and use the theme value.

Props oandregal, hellofromTonya, desrosj, costdev, pbearne, johnstonphilip, webmandesign.
Fixes #54782.