index.css

* {
  margin: 0;
  padding: 0;
  box-sizing: border-box;
}

a {
  text-decoration: none;
}

.wrapper {
  display: flex;
  align-items: center;
  justify-content: center;
  flex-direction: column;
  height: 100vh;
  background-color: gray;
}

.wrapper p {
  padding: 20px;
  font-size: 40px;
  text-shadow: 0px 2px 2px #cdd2cf;
  text-indent: 2em;
}

button {
  padding: 10px;
  font-size: 14px;
  border-radius: 4px;
  background-color: gray;
  border: #333 1px solid;
  transition: all 0.4s;
  cursor: pointer;
  outline: none;
}

button:hover {
  box-shadow: 0px 0px 0px 1px #333;
}

button:after {
  content: "提示：灰度化图片过程可能会较长，请耐心等待，请选择非微信自带浏览器，推荐谷歌。";
  position: absolute;
  width: 300px;
  /* top: calc(100% + (-350px)); */
  top: 620px;
  left: 700px;
  font-size: 14px;
  color: #333;
}

blockquote {
  position: absolute;
  top: calc(100% + (-60px));
}