#logo {
  background: none;
  padding-left: 4px;
}
#logo a {
  background-image: url(logos/2015/bah.png);
  background-size: contain;
  background-position: center center;
  background-repeat: no-repeat;
  -webkit-transition: background-image 0.5s ease-in-out;
  transition: background-image 0.5s ease-in-out;
}
body.scrolled #logo a {
  background-image: url(logos/2015/bah.png);
}