body {
  margin: 0;
}

* {
  -webkit-box-sizing: border-box;
          box-sizing: border-box;
}

#progress {
  position: fixed;
  top: 0;
  left: 0;
  right: 0;
  height: 4px;
  background-color: red;
  width: 0%;
  -webkit-transition: 20ms ease;
  transition: 20ms ease;
}

#one {
  height: 400px;
  background-color: #FFFFFF;
}

#two {
  height: 9400px;
  background-color: #242424;
}

#three {
  height: 2300px;
  background-color: #989898;
}