section:nth-child(2) {
  min-height: calc(100vh + 200px);
}

.menu {
  position: fixed;
  bottom: 0;
  left: 0;
  right: 0;
  padding: 10px;
  text-align: center;
  z-index: 1;
  display: flex;
  list-style: none;
  justify-content: center;
}

.menu li+li button {
  margin-left: 10px;
}

button {
  background: #dedede;
  font: inherit;
  border: none;
  padding: 4px 10px;
  cursor: pointer;
}

button.active {
  background: black;
  color: white;
}