.button {
  border: 2px solid red;
  background: white;
  padding: 10px;
  text-transform: uppercase;
  font-weight: bold;
  letter-spacing: 0.2em;
  position: relative;
  max-width: 100px;
}

.filler {
  content: attr(data-content);
  display: flex;
  justify-content: center;
  align-items: center;
  position: absolute;
  top: 0;
  right: 0;
  bottom: 0;
  left: 0;
  background: red;
  color: white;
  clip-path: polygon(0 0, -65% 0, 0% 100%, 0% 100%);
  transition: clip-path 0.5s;
}

.button:hover .filler,
.button:focus .filler {
  clip-path: polygon(0 0, 100% 0, 165% 100%, 0% 100%);
}