This is the CSS on the containing div. Play around with the settings for different effects.

div {
  -webkit-mask-image: linear-gradient(to bottom, rgba(0, 0, 0, 0), rgba(0, 0, 0, 1) 50%, rgba(0, 0, 0, 0));
  mask-image: linear-gradient(to bottom, rgba(0, 0, 0, 0), rgba(0, 0, 0, 1) 50%, rgba(0, 0, 0, 0));
}

Demo here