css3之animation 提交按钮简单的动画

<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Document</title>
    <style>
        *{
            padding: 0;
            margin: 0;
        }
        body{
            width: 100vw;
            height: 100vh;
            display: grid;
            grid-template: 1fr/1fr;
        }
        .btn{
            width: 200px;
            height: 50px;
            text-align: center;
            line-height: 50px;
            color:green;
            justify-self: center;
            align-self: center;
        }
        .btn::after{
            content: '';
            width: 3px;
            height: 3px;
            display: inline-block;
            animation-name: yd;
            animation-duration: 1s;
            animation-iteration-count: infinite;
        }
        @keyframes yd {
            from{
                box-shadow: none;
            }
            30%{
                box-shadow: 3px 0 0 currentColor;
            }
            60%{
                box-shadow: 3px 0 0 currentColor,9px 0 0 currentColor;
            }
            90%{
                box-shadow: 3px 0 0 currentColor,9px 0 0 currentColor,15px 0 0 currentColor;
            }
            to{
                box-shadow: 3px 0 0 currentColor,9px 0 0 currentColor,15px 0 0 currentColor;
            }
        }
    </style>
</head>
<body>
    <button class="btn">提交</button>
</body>
</html>