positioning.css

html, body, section {
  width: 100%;
  height: 100%;
}

body {
  font-family: Helvetica, Arial, sans-serif;
}

section {
  border-bottom: 1px solid black;
}

header,
footer {
  width: 100%;
  height: 40px;
  background-color: black;
  text-align: center;
  color: white;
  line-height: 40px;
}

#welcomeScreen,
#absolute {
  display: flex;
}

#welcomeScreen h1,
#absolute h1 {
  margin: auto;
  font-size: 130px;
  font-weight: bold;
  text-align: center;
}

#absolute header {
  position: absolute;
  top: 0;
}

#relative {
  position: relative;
}

#relative header,
#relative footer {
  position: absolute;
}

#relative header {
  top: 0;
}

#relative footer {
  bottom: 0;
}