Issue with Applied Visual Basics @keyframes and animation


I’m getting an “Error: Request errror: 0” in the test output area for the @keyframes and animation Properties Work lesson for the code below. I was able to complete the lesson after, “Use CSS Animation to Change the Hover State of a Button,” with no issues. Is this a bug or is something wrong with my browser or code? Thank you!

  div {
    height: 40px;
    width: 70%;
    background: black;
    margin: 50px auto;
    border-radius: 5px;

  #rect {
    animation-name: rainbow;
    animation-duration: 4s;

@keyframes rainbow {
  0% {
    background-color: blue;
  50% {
    background-color: green;
  100% {
    background-color: yellow;
<div id="rect"></div>

I’m updating this thread in case it helps someone else. It turns out it was an issue with the Firefox browser. The next lesson worked so previously I thought it was not the browser. As I was having more issues in future lessons, I decided to try Chrome and it worked.