CSS3でホバー時にLI要素の背景色を左から右に塗りつぶす方法は?

<code class="css">/* Set up the background gradient (red to blue) */
background: linear-gradient(to left, red 50%, blue 50%) right;

/* Make the background twice the size of the element */
background-size: 200% 100%;

/* Position the background to the right */
background-position: right;</code>

<code class="css">/* On hover, change the background position to the left */
background-position: left;</code>

<code class="html"><li>Hover me to fill the background</li></code>

<code class="css">li {
  display: inline-block;
  padding: 1em;
  background: linear-gradient(to left, red 50%, blue 50%) right;
  background-size: 200% 100%;
  background-position: right;
  transition: all 2s ease;
}

li:hover {
  background-position: left;
}</code>