There is a way to intervene on the generation of the css based on the theme.json file.
function update_with_dark_theme( $theme_json ){
$dark_theme = json_decode( file_get_contents( get_template_directory() . '/styles/dark.json' ), true );
return $theme_json->update_with( $dark_theme );
}
add_filter( 'wp_theme_json_data_user', 'dsfr_update_with_dark_theme' );It can be used to switch the theme scheme for e.g.
function dsfr_reload_styles(){
if ( isset( $_GET['scheme'] ) && $_GET['scheme'] == 'dark' ){
add_filter( 'wp_theme_json_data_user', 'dsfr_update_with_dark_theme' );
}
wp_enqueue_global_styles();
remove_action( 'wp_print_styles', 'print_emoji_styles' );
header( 'Content-type: text/css' );
wp_print_styles();
exit();
}
add_action( 'wp_ajax_dsfr_reload_styles', 'dsfr_reload_styles' );
add_action( 'wp_ajax_nopriv_dsfr_reload_styles', 'dsfr_reload_styles' );Source : https://fullsiteediting.com/lessons/how-to-filter-theme-json-with-php/