height

example

HTML

<div class="class-append-con">
  <div>1</div>
  <div>2</div>
  <div>3</div>
  <div>4</div>
  <div>5</div>
  <div id="six">6</div>
</div>

CSS

.class-append-con {
  height: 50px;
}
#six {
  background-color: blue;
}
.class-append-con :nth-child(-n+5) {
    height: 100%;
    background-color: black;
    color:white;
}