wp-includes/class-wp-theme-json.php:1520Returns the global styles custom CSS.
string public function get_custom_css() { _deprecated_function( __METHOD__, '6.7.0', 'get_stylesheet' ); // Add the global styles root CSS. $stylesheet = isset( $this->theme_json['styles']['css'] ) ? $this->theme_json['styles']['css'] : ''; // Add the global styles block CSS. if ( isset( $this->theme_json['styles']['blocks'] ) ) { foreach ( $this->theme_json['styles']['blocks'] as $name => $node ) { $custom_block_css = isset( $this->theme_json['styles']['blocks'][ $name ]['css'] ) ? $this->theme_json['styles']['blocks'][ $name ]['css'] : null; if ( $custom_block_css ) { $selector = static::$blocks_metadata[ $name ]['selector']; $stylesheet .= $this->process_blocks_custom_css( $custom_block_css, $selector ); } } } return $stylesheet; }Introduced in 6.2.0. Unchanged from 6.7.7 through 7.1.0.
Signature, return type and hooks compared across 5 parsed releases.
src/wp-includes/class-wp-theme-json.php, and regenerated for each WordPress release so it tracks the code rather than a snapshot of it.