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  h1 CSS Spotlight
  p background:radial-gradient() の円形グラデーションでスポットライトを形成。
  p JSでグラデーションの中心をカーソルに合わせている。
  p グラデーションのレイヤー(.spotlight)自体を移動させてしまうと調整が大変なため、 radial-gradient() の中心を移動させる手法にしている。
  h2 想定される用法
  p ビジュアル演出のほか初回アクセス時のチュートリアルなどに使える。
  p チュートリアル利用時はカーソル追従はさせず、注目点に直接当てる形が好ましい。


                body {
  font-family: -apple-system, BlinkMacSystemFont, "Helvetica Neue";
.container {
  width: 70vw;
  margin: 20px auto;
.spotlight {
  position: fixed;
  top: 0;
  left: 0;
  width: 100%;
  height: 100%;
  pointer-events: none;
  //background: rgba(#000,.4);
  background: radial-gradient(
    50px 50px //サイズ
    at //お約束
    center center,//位置
    transparent, //中央
    transparent 100px, //中央〜ボカシ
    rgba(#000,.6) 150px//ボカシ〜外周
  opacity: 0;
  animation: fadein 2s 1s 1 both;

@keyframes fadein {
  0% {opacity: 0;}
  100% {opacity: 1;}



  $('.spotlight').attr({  'style':'background:radial-gradient(50px 50px at '+ e.clientX +'px '+ e.clientY +'px, transparent, transparent 100px, rgba(0,0,0,0.6) 150px)'