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<ul>
  <li>One</li>
  <li>Two</li>
  <li>Three</li>
  <li>Four</li>
  <li>Five</li>
</ul>
body {
  color: #fff;
  font-family: sans-serif;
  margin: 0;
  padding: 0;
}

ul, li {
  margin: 0;
  padding: 0;
  list-style: none;
}

ul {
  display: flex;
  height: 100vh;
}

li {
  flex: 1;
  transition: flex 300ms ease-out, color 200ms ease-out;
  padding: 2%;
  text-align: center;
  color: rgba(255, 255, 255,0);
}

li:nth-child(1) {
  background: #f2b635;
}

li:nth-child(2) {
  background: #f19a2a ;
}

li:nth-child(3) {
  background: #49b3e8 ;
}

li:nth-child(4) {
  background: #00a0e6;
}

li:nth-child(5) {
  background: #f25648;
}

li:hover {
   flex: 3;
   color: rgba(255, 255, 255, 1);
}
Rerun