Button with Liquid Filling Effect

<!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>Liquid Filling Effect on Button</title>
    <style>
        * {
            margin: 0;
            padding: 0;
            font-family: 'Poppins', sans-serif;
        }

        body { background-color: #292929; }

        section {
            display: flex;
            justify-content: center;
            align-items: center;
            width: 100%;
            height: 100vh;
        }

        .btn {
            position: relative;
            padding: 10px 50px;
            border-radius: 30px;
            text-decoration: none;
            color: #292929;
            background-color: #ff081e;
            font-weight: bold;
            text-transform: uppercase;
            transition: 1s all ease-in-out;
            overflow: hidden;
        }

        .btn::before {
            position: absolute;
            content: '';
            width: 400px;
            height: 400px;
            background-color: #ececec;
            top: -370px;
            left: -120px;
            border-radius: 45%;
            transition: 2s all ease-in-out;
            animation: wave 10s infinite linear;
        }

        .btn::after {
            position: absolute;
            content: '';
            width: 400px;
            height: 400px;
            background-color: #ececec80;
            top: -360px;
            left: -125px;
            border-radius: 45%;
            transition: 2s all ease-in-out;
            animation: wave 9s infinite linear;
        }

        .btn span {
            position: relative;
            z-index: 1;
        }

        .btn:hover {
            color: #fff;
        }

        .btn:hover::before {
            top: -450px;
        }

        .btn:hover::after {
            top: -440px;
        }

        @keyframes wave {
            0% {
                transform: rotate(0deg);
            }

            100% {
                transform: rotate(360deg);
            }
            
        }
        
    </style>
</head>
<body>
    <section>
        <a href="" class="btn">
            <span>
                Subscribe!
            </span>
        </a>
    </section>
</body>
</html>
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Result Screenshot(s)

Button with Liquid Filling EffectWorking Sample0