SOURCE

<div>
  <input type="text" />
  <span>Next</span>
</div>

div {
  background:red;
  font-size:0;
}
input{
  float:left;
  height:30px;
  border:none;
  outline:none;
}
span {
  float:left;
  font-size:12px;
  background:rgba(100,100,100,1);
  line-height:30px;
  height:30px;
  display:inline-block;
}

input:focus + span {
  background:rgba(100,100,100,.5);
}