Answers for "transition fade"

css fade div

ol {
  border   : 1px #d8d8d8 dashed;
  position : relative;
}

ol:after {
  content  : "";
  position : absolute;
  z-index  : 1;
  bottom   : 0;
  left     : 0;
  pointer-events   : none;
  background-image : linear-gradient(to bottom, 
                    rgba(255,255,255, 0), 
                    rgba(255,255,255, 1) 90%);
  width    : 100%;
  height   : 4em;
}

css opacity transition

div {
  transition: opacity seconds;
}