MediaWiki:Common.css

/* CSS placed here will be applied to all skins */
body {
background-image: URL("http://test.medievalengineers.com/wp-content/uploads/2016/12/Website-Background9.jpg");
}
#mw-head{
background-color:#000;
}
#mw-panel{
color:white;
}
a{
color:orange;
}