<div class="a"></div>
<div class="test">
  conteudo
</div>

* {
  margin: 0;
  padding: 0;
  box-sizing :border-box;
}

.a {
  background: red;
  height: 100px;
  width: 100px;
}


.test {
  display: flex;
  align-items: center;
  justify-content: center;
  height: 100px;
  width: 100px;
  position: relative;
}

.test:before {
  content: '';
  height: 50%;
  width: 100%;
  display: block;
  z-index: -1;
  position: absolute;
  background: red;
  top: 0;
}