preg_replace(): Compilation failed: regular expression is too large at offset ...

There is an error in cssmgr.php:164 :

    if (preg_match('/@media/',$CSSstr)) { 
        preg_match_all('/@media(.*?)\{(([^\{\}]*\{[^\{\}]*\})+)\s*\}/is',$CSSstr,$m);
        for($i=0; $i<count($m[0]); $i++) {
            if ($this->mpdf->CSSselectMedia && !preg_match('/('.trim($this->mpdf->CSSselectMedia).'|all)/i',$m[1][$i])) { 
                $CSSstr = preg_replace('/'.preg_quote($m[0][$i],'/').'/','',$CSSstr);
            }
            else {
                $CSSstr = preg_replace('/'.preg_quote($m[0][$i],'/').'/',' '.$m[2][$i].' ',$CSSstr);
            }
        }
    }

On large CSS files with complicated rules it may cause regexp limit when replacing by preg_replace:

exception 'yii\base\ErrorException' with message 'preg_replace(): Compilation failed: regular expression is too large at offset 70187' in .../vendor/kartik-v/mpdf/classes/cssmgr.php:164

... but (as far as I can see) there is no real need in preg_replace() in this place. We have exact text, matched by preg_match_all() and now we can use str_replace() (or mb_str_replace()) to clear it out.

P.S. I don't offer pull request because I can miss something

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kartik-v / mpdf

preg_replace(): Compilation failed: regular expression is too large at offset ... #4