Cara menggunakan php preg_replace unicode

So i'm not still really familiar with regex and how does it work, but i have issue with my code. I have ¤ in my text and it gets replace with unicode ? block. //en.wikipedia.org/wiki/Specials_[Unicode_block] for me and I don't get why.

Here is the code I'm using.

#kool { width:800px; border:groove; margin:0 auto; padding:25px; }