SCSS

by jonaspraem

HTML

<button>Hover to change color</button>

SCSS

$blue: #0084ff;
$blue-darker: darken($blue, 5);

@keyframes mymove {
    0% {width: 0%}
    100%  {width: 80%}
}

body {
  background: #20262E;
  padding: 20px;
  font-family: Helvetica;
}
button {
  margin: auto;
  background-color: $blue;
  border: 1px solid $blue;
  border-radius: 5px;
  padding: 8px 14px;
  font-size: 15px;
  color: #fff;
  cursor: pointer;
  position: relative;
   &:hover {
    &:after {
      content: "";
      position: absolute;
      bottom: 3px;
      width: 80%;
      height: 2px;
      background-color: white;
      left: 0;
      right: 0;
      margin: auto;
      animation-name: mymove;
      animation-duration: .5s;
     }
  }
}