div,
header,
main,
aside,
footer {
  position: relative;
  box-sizing: border-box;
}

.sticky-top {
  position: sticky;
  top: 0;
  z-index: 8;
}

.display--toggle {
  display: none;
  visibility: hidden;
}

img {
  display: block;
  max-width: 100%;
  height: auto;
}