.bg {
  background: #000;
  width: 100%;
  height: 100px;
  opacity: 0;
}

.show {
  opacity: 0.4;
}

.transition {    
  -webkit-transition: all 0.4s ease-in-out;
  -moz-transition: all 0.4s ease-in-out;
  -o-transition: all 0.4s ease-in-out;
  transition: all 0.4s ease-in-out;
}

.fixed {
  position: fixed;
  top: 0;
  left: 0;
  width: 100%;
  z-index: 1;
}


.down {
  top: 150px;
}

.up {
  font-size: 0px;
  top: 500px;
}