html,
body {
    height: 100%;
    width: 100%;
    background-color: rgba(31,31,31, .8) !important;
}

body {
    display: -ms-flexbox;
    display: flex;
    -ms-flex-align: center;
    align-items: center;
    padding-top: 40px;
    padding-bottom: 40px;
}

.form-signin {
    width: 100%;
    max-width: 800px;
    padding: 15px;
    margin: auto;
}
.max-w-sm {
    width: 550px;
}
.img-logomarca {
    max-width: 20% !important;
}
@media (min-width: 720px) {
    .max-w-sm {
        width: 100% !important;
    }
    .img-logomarca {
        max-width: 50% !important;
    }
}
@media (max-width: 500px) {
    .max-w-sm {
        width: 100% !important;
    }
    .img-logomarca {
        max-width: 50% !important;
    }
}