W3Schools Tryit Editor

<!DOCTYPE html>
<html>
<head>
<style>
  #frameDiv {
    width: 300px;
    height: 300px;
    margin: 20px;
    position: relative;
    border: solid black 1px;
    overflow: hidden;
    background-color: rgb(205, 242, 205);
  }

svg {
    position: absolute;
    top: 0;
    left: 0;
    width: 100%;
    height: 100%;
  }

path {
    opacity: 0.3;
  }

img {
    position: absolute;
    z-index: 1;
    width: 70px;
    offset-path: path('M 50,150 C 50,275 250,275 250,150 M 250,150 C 250,25 50,25 50,150');
    animation: moveDiv linear 7s infinite;
  }

@keyframes moveDiv {
    100%  { offset-distance: 100%; }
  }
</style>
</head>
<body>

<h1>Change the offset property value with JavaScript</h1>

<p>Initially, the fish follows a circular path and is rotated in the direction it is moving.</p>

<p>Click the "Try it" button to change the offset property of the fish element so that:</p>
<ol>
  <li>the path changes (offset-path)</li>
  <li>the fish starts the animation at a 200 pixels distance from the start of the path (offset-distance)</li>
  <li>the fish is rotated to be perpendicular (90 degrees) to the direction it is moving (offset-rotate)</li>
</ol>

</body>
</html>