.header_principal{
    text-align:center;  
    
    border-bottom:1px solid #cdcdcd;
}
.header_principal svg{
    max-width:300px;
}

.contenu_principal{
    padding:20px 0;
    /* background:url('https://www.ms-vacances.com/files/site/data/visuel.jpg') no-repeat 50% 50%; */
    background:#f4f4f4;
    min-height:600px;
}
.form-group{
    margin-bottom:15px;
}

.message_error_connexion{
    color:red;
    font-weight:bold;
}