<!-- Forum question answer only -->
<!-- not a real demo -->
<section class="animation-box">
  <span class="text">THIS</span>
  <span class="square1"></span>
  <span class="text2">THAT</span><br>
</section>

<!-- my version -->
<p class="animate"><span>This</span><span>That</span< /p>

body {
  background: #666;
}
.animation-box {
  min-height: 4.5rem;
  margin: 175px auto 0;
  display: flex;
  align-items: center;
  width: 100%;
  overflow: hidden;
}
.animation-box span {
  opacity: 1;
  animation: leftFadeInOut 18.5s ease 2.75s forwards;
}
.text {
  font-size: 30px;
  color: #000;
}
.square1 {
  width: 1.75vw;
  height: 1.75vw;
  background-color: #ccc;
  margin: auto;
}
.text2 {
  font-size: 30px;
  color: #fff;
}
/*
@keyframes leftFadeInOut {
  0%,
  33% {
    position: absolute;
    left: 1rem;
    opacity: 0;
  }
  75% {
    position: absolute;
    left: 40rem;
    opacity: 1;
  }
  100% {
    position: absolute;
    left: 79.5rem;
    opacity: 0;
  }
}
*/
/* note it would be better to use transform rather than left as transform is more performant. Also avoid the use of magic numbers such as 79.5rem */

/* My version */
.animate {
  min-height: 4.5rem;
  margin: 75px 0 0;
  display: flex;
  align-items: center;
  animation: slide 18.5s ease 2.75s;
}
.animate span {
  font-size: 30px;
  color: #000;
  text-transform: uppercase;
  order: 1;
}
.animate:before {
  content: "";
  width: 1.75vw;
  height: 1.75vw;
  background-color: #ccc;
  margin: auto;
  order: 2;
}
.animate span:last-child {
  color: #fff;
  order: 3;
}
@keyframes slide {
  0% {
    width: 0%;
    opacity: 0;
  }
  100% {
    width: 100%;
    opacity: 1;
  }
}