.wp-block-button__link {
  -webkit-transform: perspective(1px) translateZ(0);
  transform: perspective(1px) translateZ(0);
  box-shadow: 0 0 1px rgba(0, 0, 0, 0);
  position: relative;
  -webkit-transition-property: color;
  transition-property: color;
  -webkit-transition-duration: 0.3s;
  transition-duration: 0.3s;
}
.wp-block-button__link:before {
  content: "";
  position: absolute;
  z-index: -1;
  top: 0;
  left: 0;
  right: 0;
  bottom: 0;
  background: #000;
  -webkit-transform: scaleX(0);
  transform: scaleX(0);
  -webkit-transform-origin: 0 50%;
  transform-origin: 0 50%;
  -webkit-transition-property: transform;
  transition-property: transform;
  -webkit-transition-duration: 0.3s;
  transition-duration: 0.3s;
  -webkit-transition-timing-function: ease-out;
  transition-timing-function: ease-out;
}

.wp-block-button__link:hover:before, .wp-block-button__link:focus:before, .wp-block-button__link:active:before {
  -webkit-transform: scaleX(1);
  transform: scaleX(1);
}