body {
  margin: 0;
  box-sizing: border-box;
}

header {
  position: fixed;
  top: 0;
  left: 0;
  font: bold 20pt monospace;
  width: 100%;
  padding: 8px 16px;
}

section {
  height: 80dvh;
  display: grid;
  place-items: center;
}

section:nth-of-type(even) {
  background: #000;
  color: #fff;
}

a {
  all: unset;
  display: block;
  padding: 8px 16px;
  font: 20pt monospace;
  position: fixed;
  bottom: 0;
  right: 0;
  background: lightblue;
  border-radius: 5px;
  text-decoration: underline;
  color: hotpink;
  cursor: pointer;
  margin: 16px;
}

.callback-counter-display {
  padding: 8px 16px;
  font: 20pt monospace;
  position: fixed;
  top: 0;
  right: 0;
  margin: 16px;
  background: #fff;
}