body {
            background: #f2f2f2;
            min-height: 100vh;
            display: flex;
            align-items: center;
            justify-content: center;
            font-family: 'Segoe UI', sans-serif;
        }
        .card {
            width: 420px;
            border-radius: 18px;
            box-shadow: 0 4px 12px rgba(0,0,0,0.1);
            border: none;
        }
        .card-header {
            background: #1a1a1a;
            color: white;
            border-radius: 16px 16px 0 0 !important;
            text-align: center;
            padding: 1.4rem;
        }
        .btn-dark {
            background: #1a1a1a;
            border: none;
        }
        .is-invalid { 
            border-color: #dc3545 !important;
        }
        .invalid-feedback {
            display: block;
            width: 100%;
            margin-top: 0.25rem;
            font-size: 0.875em;
            color: #dc3545;
        }