<button class="create-button">
  <span>Create Button</span>
</button>

* {
  margin: 0;
  padding: 0;
}
body, html {
  height: 100%;
  background: #1d1e22;
}
.create-button {
  font-family: monospace;
  font-weight: bold;
  text-transform: uppercase;
  background: #000;
  color: #fff;
  border: none;
  border-radius: 0;
  position: absolute;
  left: 50%;
  top: 50%;
  position: relative;
  transform: translate(-50%,-50%);
  border-radius: 3px;
  cursor: pointer;
  padding: 0.8em 1.6em;
  font-size: 18px;
  overflow: hidden;
  &:focus, &:active {
    outline: none;
  }
  &:before, &:after {
    content: '';
    position: absolute;
    bottom: 0;
    top: 0;
    left: 0;
    right: 0;
    height: auto;
    width: auto;
    z-index: -1;
    border-radius: inherit;
    background: inherit;
  }
  &:before {
    background: linear-gradient(90deg, #0ebeff, #ffdd40, #ae63e4, #47cf73, #0ebeff, #ffdd40, #ae63e4, #47cf73);
    background-size: 200% 200%;
  }
  &:after {
    margin: 3px;
  }
  &:hover:before, &:focus:before {
    animation: rainbow-border 1.5s linear infinite
  }
}
@keyframes rainbow-border {
  0% { background-position: 0% 50% }
  100% { background-position: 200% 50% }
}