public function get_precompiled_css_content() {
        $configs = [$this] + $this->parent_configs;
        $css = '';

        foreach ($configs as $config) {
            if (isset($config->precompiledcsscallback)) {
                $function = $config->precompiledcsscallback;
                if (function_exists($function)) {
                    $css .= $function($this);
                }
            }
        }
        return $css;
    }