JSFiddle - React, Tailwind, and code Playground

HTML

<link rel="stylesheet" href="//maxcdn.bootstrapcdn.com/font-awesome/4.1.0/css/font-awesome.min.css">
<div id="mainicons">
  <a href="/"><i class="fa fa-home"></i><span>Home</span></a>
  <a href="/ask"><i class="fa fa-envelope"></i><span>Ask</span></a>
  <a href="/submit"><i class="fa fa-pencil "></i><span>Request</span></a>
  <a href="/archive"><i class="fa fa-clock-o"></i><span>Archive</span></a>
</div>

CSS

#mainicons {
  position: fixed;
  top: 250px;
  left: 0px;
  text-align: center;
  display: flex;
  flex-direction: column;
}

#mainicons>a {
  position: relative;
  display: flex;
  justify-content: center;
  align-items: center;
}

#mainicons i {
  opacity: 1;
  height: 40px;
  width: 50px;
  padding: 10px;
  color: white;
  background: black;
  text-align: center;
  font-size: 15px;
  line-height: 40px;
  transition: all .5s ease;
}

#mainicons i:hover {
  border: 1.5px solid black;
  color: black;
  background: white;
}

#mainicons span {
  color: black;
  background: white;
  width: 70px;
  font-size: 15px;
  transition: all .5s ease;
  position: absolute;
  height: 100%;
  display: flex;
  align-items: center;
  justify-content: center;
  left: -100px;
  opacity: 0;
}

#mainicons a:hover>span {
  opacity: 1;
  left: 70px;
  transition: .5s;
    border: 1px solid black;
}