body {
    position: relative;
    height: 100vh;
    width: 100%;
    background: url("images/anasayfa_foto.jpg");
    background-position: center;
    background-size: cover;
    background-repeat: no-repeat;
}

.alert.alert-success {
    color: white;
    background-color: #00bcd4;
    padding: 15px;
    margin-bottom: 10px;
    border: 1px solid #00bcd4;
    text-align: center;
    width: 100%;
    margin-left: auto;
    margin-right: auto;
    font-size: 20px
}

@media (max-width: 768px) {
    body {
        position: relative;
        height: 100vh;
        width: 100%;
        background: url("images/mobil.jpg");
        background-position: center;
        background-size: cover;
        background-repeat: no-repeat;
    }

    .alert.alert-success {
        color: white;
        background-color: #00bcd4;
        padding: 15px;
        margin-bottom: 10px;
        border: 1px solid #00bcd4;
        text-align: center;
        width: 100%;
        margin-left: auto;
        margin-right: auto;
        font-size: 15px
    }
}