Problems with @charset in CSS

I think I've found two small bugs.

In private function processAtRulesAndSelectors($css)
https://github.com/litespeedtech/lscache_wp/blob/master/litespeed-cache/lib/css_min.class.php#L701

// @charset handling
if (preg_match($this->charsetRegex, $css, $matches)) {
        // Keep the first @charset at-rule found
        $charset = $matches[0];
        // Delete all @charset at-rules
        $css = preg_replace($this->charsetRegex, '', $css);
}

But $matches is not defined in that function. So the first @charset is replaced

Secondly, in https://github.com/litespeedtech/lscache_wp/blob/master/litespeed-cache/inc/optimizer.class.php#L149

Has the regex

$data = preg_replace( '/@charset[^;]+;\\s*/', '', $data ) ;

This is incorrect. It should end ;\s*/ the double slash causes it to fail. See https://www.phpliveregex.com/p/ujR#tab-preg-replace for a demo

Basically, I think that @charset should not be removed from the start of a file. But I think these two functions don't work as intended.

Sorry if I haven't explained this well!

Start in litespeed-cache/lib/css_min.class.php at processAtRulesAndSelectors($css), then inspect litespeed-cache/inc/optimizer.class.php around line 149. Reproduce both @charset cases with the CSS processing paths and confirm the intended handling from the issue; done means the two functions behave consistently without incorrectly removing or replacing @charset rules.