body {
    min-height: 100vh;
    display: grid;
    place-items: center;
    background: linear-gradient(135deg, #eef2f7, #dfe1e5);
}
body.dark {
    background: linear-gradient(135deg, #2b2b2b, #1e1e1e);
}
.login-card {
    width: 100%;
    max-width: 420px;
}
@media (min-width: 768px) {
    .login-card {
        max-width: 500px;
    }
}
.card {
    border-radius: 16px;
    box-shadow: 0 0.5rem 1rem rgba(0,0,0,0.1);
}
body.dark .card {
    background-color: #343a40;
    color: #f8f9fa;
}
body.dark .form-control,
body.dark .form-check-input {
    background-color: #495057;
    color: #f8f9fa;
    border-color: #6c757d;
}
.alert.validation-summary-valid {
    display: none;
}