CSS Minification Removes Space in :nth-child(of <selector>), Causing Invalid CSS

[Presskopp]

see wp-media/wp-rocket#7363 (reported by @rosamillan)

I think this can be addressed by changing

$content = preg_replace('/:(' . implode('|', $pseudos) . ')\(\s*([+-]?)\s*(.+?)\s*([+-]?)\s*(.*?)\s*\)/', ':$1($2$3$4$5)', $content);

in CSS.php, function stripWhitespace($content) (~ L.758)

to

$content = preg_replace('/:(' . implode('|', $pseudos) . ')\(\s*([+-]?)\s*(.+?)\s*([+-]?)\s*(.*?)\s*(of\s+[^\)]+)?\s*\)/', ':$1($2$3$4$5$6)', $content);

[Presskopp]

uh, sorry I din't notice #426