BuddyPress.org

O.K., I got it:

you need to overwrite each CSS-line from the original base.css file:

#header h1 a {

background: url(../images/logo.jpg) no-repeat;

overflow: hidden;

width: 1088px;

height: 142px;

display: block;

margin:0px auto;

text-indent: none;

float: none;

}