// button
@keyframes buttonEffect {
  to {
    opacity: 0;
    top: -6px;
    left: -6px;
    bottom: -6px;
    right: -6px;
    border-width: 6px;
  }
}
// normal btn, primary btn
.next-btn-normal.btn-animate:before,
.next-btn-primary.btn-animate:before {
  border-color: $color-brand1-6;
}
// next-btn-secondary btn
.next-btn-secondary.btn-animate:before {
  border-color: $color-warning-3;
}
// error btn
.next-btn-warning.btn-animate:before {
  border-color: $color-error-3;
}

.btn-animate:before {
  content: ' ';
  position: absolute;
  top: -1px;
  left: -1px;
  bottom: -1px;
  right: -1px;
  border-radius: inherit;
  border: 0 solid transparent;
  opacity: 0.4;
  -webkit-animation: buttonEffect 0.4s;
  animation: buttonEffect 0.4s;
  display: block;
}