Cesium polyline entity fade

HTML

<link rel="stylesheet" href="https://cesiumjs.org/Cesium/Build/Cesium/Widgets/widgets.css">
<script src="https://cesiumjs.org/Cesium/Build/CesiumUnminified/Cesium.js"></script>
<div id="cesiumContainer"></div>

CSS

html, #cesiumContainer {
          height: 100%;
      }
      body {
          padding: 0;
          margin: 0;
          overflow: hidden;
          height: 100%;
      }