/* default: mobile/tablet where sidebar isn't fixed/left */
.full-width-banner {
  width: 100%;
}

.full-width-banner img {
  width: 100%;
  height: auto;
  display: block;
  border-radius: 0;
}

/* desktop: sidebar becomes fixed and takes 16rem */
@media (min-width: 768px) {
  .full-width-banner {
    margin-left: 16rem;
    width: calc(100% - 16rem);
  }
}