Ah, not modern skin not has logo, so you can add that line to
MediaWiki:Monobook.css
2013/2/19 devunt <devunt(a)gmail.com>om>:
You can add this code in each skin's css file
(ex:
MediaWiki:Vector.css, MediaWiki:Modern.css)
#p-logo a { background-image:
url('http://www.example.com/w/logo_you_want.png') !important; }