<botton class="btn">Contact us</botton>

<a class="link" href="#">Contact us</a>

body {
  margin: 0;
  background-color: #343a40;
  min-width: 100vw;
  min-height: 100vh;
  display: flex;
  flex-flow: column wrap;
  align-items: center;
  justify-content: center;
  > * {
    margin: 1rem
  }
}

p {
  color: #fff;
}

// ------------------------------------------
// btn
// ------------------------------------------
$btn-bg: #fff;
$btn-hover-bg: #3b5bdb;
$btn-color: #000;
$btn-hover-color: #fff;

.btn {
  padding: 1em 1.5em;
  background-color: $btn-bg;
  cursor: pointer;
  border-radius: 3px;
  overflow: hidden;
  color: rgba(0, 0, 0, 0);
  text-shadow: 0 0 0 $btn-color, 0 3rem 0 $btn-hover-color;
  transition: background-color 150ms, text-shadow 200ms;
  font-size: 1.1rem;
  &:hover {
    background-color: $btn-hover-bg;
    text-shadow: 0 -3rem 0 $btn-color, 0 0 0 $btn-hover-color;
  }
}

// ------------------------------------------
// Link
// ------------------------------------------
$link-color: #748ffc;
$link-hover-color: #fff;
.link {
  display: inline-block;
  text-decoration: none;
  cursor: pointer;
  overflow: hidden;
  color: rgba(0, 0, 0, 0);
  text-shadow: 0 0 0 $link-color, 0 3rem 0 $link-hover-color;
  transition: text-shadow 200ms;
  vertical-align: bottom;
  &:hover {
    text-shadow: 0 -3rem 0 $link-color, 0 0 0 $link-hover-color;
  }
}