11.4 cloude> /* 天空轮播晴朗阴晴朗 */ *{ margin: 0; padding: 0; }

<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta http-equiv="X-UA-Compatible" content="IE=edge">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Document</title>
    <style>
        /* 天空轮播 晴朗 阴 晴朗 */
        *{
            margin: 0;
            padding: 0;
        }
        .parent{
            /* vh viewheight 浏览器视口区域高度 vw viewwidth 视口区域宽度 */
            height: 100vh;
            background-color: skyblue;
            animation: sky 10s linear infinite;
        }
        /* 定义一个天空动画 */
        @keyframes sky {
            0%{
                background-color: skyblue;
            }
            50%{
                background-color: #000;
            }
            100%{
                background-color: skyblue;
            }
            
        }
        .cloud_one{
            width: 300%;
            height: 600px;
            margin: 30px auto;
            background: url(../images/cloud_one.png) repeat-x;
            position: fixed;
            left: 0;
            top: 0;
            animation: cloud 20s linear infinite;
        }
        .cloud_two{
            width: 300%;
            height: 600px;
            margin: 30px auto;
            background: url(../images/cloud_two.png) repeat-x;
            position: fixed;
            left: 0;
            top: 0;
            animation: cloud 40s linear infinite;
        }
        .cloud_three{
            width: 300%;
            height: 600px;
            margin: 30px auto;
            background: url(../images/cloud_three.png) repeat-x;
            position: fixed;
            left: 0;
            top: 0;
            animation: cloud 60s linear infinite;
        }
        @keyframes cloud {
            from{
                left: 0;
            }
            to{
                left: -200%;
            }
            
        }
    </style>
</head>
<body>
    <div class="parent">
        <div class="cloud_one"></div>
        <div class="cloud_two"></div>
        <div class="cloud_three"></div>
    </div>
</body>
</html>