Unable to show color fill animation in div when the page loads

Question

$("#whoami").waypoint(function() {
    console.log('you have scrolled to the h1!');
   });

.d8{
    border: 1px solid black;
    width: 100%;
    height: 2.5rem;
    margin-left: 5rem;
    border-radius: 1rem;
    background: linear-gradient(to right, #e74c3c 85%, #FFF 50%);
}

<div class="d8"></div>

Now I have been trying to fill the color in the div when the waypoint reaches the particular section having some nice animation effect for the user and I am not able to achieve it though, Have tried transition effect and keyframe none seems to work, any help would be very much appreciated.

Answer 1

In you case you can animate background-size instead of background-image (that you cannot animate) and make the linear-gradient to be one color as the white part will be the part without background:

.d8 {
  border: 1px solid black;
  width: 80%;
  height: 2.5rem;
  margin-left: 5rem;
  border-radius: 1rem;
  background-image: linear-gradient(to right, #e74c3c, #e74c3c);
  background-size: 80% 100%;
  background-repeat: no-repeat;
  transition: 0.5s;
}

.d8:hover {
  background-size: 100% 100%;
}

<div class="d8"></div>