JSFiddle - React, Tailwind, and code Playground

HTML

<div class="outercontainer">
  <div class="optioncontainer">
    <div class="optionlist">
      <li class="listitem" id="red">Red</li>
      <li class="" id="blue">Blue</li>
      <li class="listitem" id="green">Green</li>
      <li class="listitem" id="yellow">Yellow</li>
      <li class="listitem" id="orange">Orange</li>
      <li id="white">White</li>
      <li id="black">Black</li>
    </div>
  </div>
</div>

CSS

/* Start Miscellaneous stuff */

body {
  background: #131418;
  color: #999;
  text-align: center;
}

.optionlist a {
  color: #999;
  text-decoration: none;
}

@keyframes mycoolfadeout {
  from {
    opacity: 1;
  }
  to {
    opacity: 0;
  }
}

@keyframes mycoolfadein {
  from {
    opacity: 0;
  }
  to {
    opacity: 1;
  }
}


/* End Miscellaneous stuff */

.outercontainer {
  border: 1px solid blue;
  /*This needs to be in the middle of the screen and everthing should fit inside it*/
  position: fixed;
  /*border to highlight only - not part of final product*/
  top: 50%;
  left: 50%;
  transform: translate(-50%, -50%);
  width: 1200px;
  max-width: 80vw;
  height: 600px;
  max-height: 70vh;
}

.optioncontainer {
  width: 250px;
  max-width: 20vw;
}

.optionlist li {
  background: #fff;
  padding: .5em;
  box-shadow: inset 10px 10px 100px 25px rgba(0, 0, 0, .8);
  list-style-type: none;
}

.optionlist li:nth-child(odd) {
  background: #000;
}

.optionlist li:hover {
  background: red;
}

.optionlist li:hover::after {
  /* The part the needs to be fixed */
  animation: mycoolfadein 1s;
  display:block;
}


/* Start Background Control */

.listitem::after {
  content: "";
  width: 80vw;
  height: 70vh;
  background-image: url(http://lorempixel.com/800/600/);
  background-size: 80vw 70vh;
  position: fixed;
  top: 50%;
  left: 50%;
  display:none;
  transform: translate(-50%, -50%);
}


/* End Background Control */