<button class="favorite styled" type="button">Add to favorites</button>

.styled {
  border: 0;
  line-height: 2.5;
  padding: 0 20px;
  font-size: 1rem;
  text-align: center;
  color: #fff;
  text-shadow: 1px 1px 1px #000;
  border-radius: 10px;
  background-color: rgba(220, 0, 0, 1);
  background-image: linear-gradient(
    to top left,
    rgba(0, 0, 0, 0.2),
    rgba(0, 0, 0, 0.2) 30%,
    rgba(0, 0, 0, 0)
  );
  box-shadow:
    inset 2px 2px 3px rgba(255, 255, 255, 0.6),
    inset -2px -2px 3px rgba(0, 0, 0, 0.6);
}

.styled:hover {
  background-color: rgba(255, 0, 0, 1);
}

.styled:active {
  box-shadow:
    inset -2px -2px 3px rgba(255, 255, 255, 0.6),
    inset 2px 2px 3px rgba(0, 0, 0, 0.6);
}