div:has(.separator) {
  position: sticky;
  top: 39px;
}
.separator {
  display: block;
  padding-top: 4px;
  border: 0 solid #fff;
  background: #fff;
  box-sizing: border-box;
  border-top-width: 4px;
  border-bottom-width: 4px;
}
.separator:empty {
  display: block;
}