* {
  margin: 0;
  padding: 0;
  box-sizing: border-box;
}

#wonder {
  position: absolute;
  width: 100%;
  height: 600px;
  left: 0;
  top: 0;
  z-index: -1;
  background: #3F51B5;
}

@media screen and (max-width: 600px) {
  #wonder {
    height: 500px;
  }
}