.invisible {
  transition: opacity 3s ease;
  opacity: 0.0;
}

.visible {
  transition: opacity 3s ease;
  opacity: 1.0;
}

.box-lg {
  height: 100vh;
  border: 1px dotted grey;
}

h1 {
  text-align: center;
  }

section {
  height: 90vh;
  width: 250vw;
  display: flex;
  justify-content: center;
  align-items: center;
  background-color: lightgrey;
  position: absolute;

}