div#slide1,
div#slide2,
div#slide3 { 
  position: absolute;
  left: 0px;
  top: 179px;
  width: 660px;
  height: 410px;
  /*background: #ff00ff;*/
  background-repeat: no-repeat;
}

div#slide1 { 
  background: url('../img/visualization.png');
  opacity: 1;
}

div#slide2 { 
  background: url('../img/web_design.png');
  opacity: 0;
}

div#slide3 { 
  background: url('../img/web_development.png');
  opacity: 0;
}