b站视频演示效果：
效果图：
完整代码：
<!DOCTYPE html>
<html lang="en">
<head>
<meta charset="UTF-8">
<meta name="viewport" content="width=device-width, initial-scale=1.0">
<title>背景渐变动画登录页</title>
<style>
* {
margin: 0;
padding: 0;
box-sizing: border-box;
font-family: "Quicksand", sans-serif;
}
body {
display: flex;
justify-content: center;
align-items: center;
min-height: 100vh;
background: linear-gradient(-45deg, #ee7752, #e73c7e, #23a6d5, #23d5ab);
background-size: 400% 400%;
