PostCSS has XSS via Unescaped </style> in its CSS Stringify Output

PostCSS: XSS via Unescaped in CSS Stringify Output Summary PostCSS v8.5.5 latest does not escape sequences when stringifying CSS ASTs. When user-submitted CSS is parsed and re-stringified for embedding in HTML tags, in CSS values breaks out of the style context, enabling XSS. Proof of Concept...