html, body {
    height: 100%;
}

body {
    display: -ms-flexbox;
    -ms-flex-align: center;
    -ms-flex-pack: center;
    -webkit-box-align: center;
    align-items: center;
    -webkit-box-pack: center;
    justify-content: center;
    background: url("bg.png") no-repeat center fixed;
    -webkit-background-size: cover;
    background-size: cover;

    top: 5%;
    position: relative;
}

.container {
    max-width: 500px;
    background: rgba(255, 255, 255, 0.15); /* Transparenz */
    backdrop-filter: blur(10px); /* schöner Glas-Effekt */
    -webkit-backdrop-filter: blur(10px);
    padding: 30px;
    border-radius: 15px;
    box-shadow: 0 0 30px rgba(0,0,0,0.5);
}