Why doesn't the background-position attribute work here

Question

I have created a moving sphere animation using CSS and I don't get why background-position doesn't work in the second one one. In the first one, I wrote background-size: 150% 150%; and in the second one I wrote background-size: 100% 100%;.

Why is this happening???

The links to my codepens: -https://codepen.io/theanonymouskoder/pen/eYWWZzE?editors=0100 -https://codepen.io/theanonymouskoder/pen/BaRRKpN?editors=0100

The code

* {
  margin: 0px;
  padding: 0px;
}

body {
  background: black;
  overflow: hidden;
}

.sphere {
  width: 500px;
  height: 500px;
  border-radius: 50%;
  margin: 10px;
  background: radial-gradient(
    #ffff00,
    #774400
  );
  background-size: 150% 150%;
  animation: turn 3s ease infinite;
}

@keyframes turn {
  0% {
    background-position: 10% 10%;
  }
  50% {
    background-position: 90% 90%;
  }
  100% {
    background-position: 10% 10%;
  }
}

<div class = 'sphere'>
  This works nicely
</div>

* {
  margin: 0px;
  padding: 0px;
}

body {
  background: black;
  overflow: hidden;
}

.sphere {
  width: 500px;
  height: 500px;
  border-radius: 50%;
  margin: 10px;
  background: radial-gradient(
    #ffff00,
    #774400
  );
  background-size: 100% 100%;
  animation: turn 3s ease infinite;
}

@keyframes turn {
  0% {
    background-position: 10% 10%;
  }
  50% {
    background-position: 90% 90%;
  }
  100% {
    background-position: 10% 10%;
  }
}

<div class = 'sphere'>
  This works nicely
</div>