CSS de nitidez de linha

hr.hr-1 {
  margin: 100px;
  border: 0;
  height: 1px;
  background-image: linear-gradient(
    to right,
    rgba(0, 0, 0, 0),
    rgba(0, 0, 0, 0.75),
    rgba(0, 0, 0, 0)
  );
}
Blue Baboon