<!DOCTYPE html>
<html>
  <head>
    <title>CSS Motion Path: ray paths with contain</title>
    <style>
      #container {
        width: 250px;
        height: 250px;
        transform: translate(100px);
      }
      #target {
        position: relative;
        left: 50px;
        top: 50px;
        width: 150px;
        height: 25px;
        background-color: lime;
        /*
         * The original path length is 50px, which is not enough to contain
         * the element entirely, so it should be increased.
         * "75px" is just the center of the element, which makes the path
         * length increase minimally.
         * Besides, -75px = (-150px * 2) + 225px, the used offset distance is
         * -225px in this case.
         * Note: offset-anchor is "200% -300%", and ray angle is -90deg.
         */
        transform: translate(calc(-75px), calc(25px * 3));
      }
    </style>
  </head>
  <body>
    <div id="container">
      <div id="target"></div>
    </div>
  </body>
</html>