效果

实现

html

<!DOCTYPE html>
<html lang="en">
  <head>
    <meta charset="UTF-8" />
    <meta name="viewport" content="width=device-width, initial-scale=1.0" />
    <title></title>
    <link rel="stylesheet" href="./index.css" />
  </head>
  <body>
    <div class="box">
      <div class="btn"></div>
      <div class="light">
        <div class="base main"></div>
        <div class="base bg"></div>
      </div>
    </div>
  </body>
</html>

css

body,
html {
  margin: 0;
  padding: 0;
  width: 100vw;
  height: 100vh;
  display: flex;
  justify-content: center;
  align-items: center;
  background-color: rgba(0, 0, 0, 0.5);
  overflow: hidden;
}

.box {
  position: relative;
}

.box .btn {
  position: absolute;
  top: -250px;
  left: -50px;
  width: 100px;
  height: 50px;
  border-radius: 20px;
  background-color: #fff;
  cursor: pointer;
  transition: all 0.5s;
}

.box .light .base {
  width: 300px;
  height: 300px;
  border-radius: 50%;
  position: absolute;
  top: 50%;
  left: 50%;
  transform: translate(-50%, -50%);
  transition: all 0.5s;
}

.box .btn:hover + .light > .main {
  background-color: #fff;
}

.box .btn:hover + .light > .bg {
  filter: blur(50px);
  z-index: 20;
  background: rgba(255, 255, 255, 0.8);
}