@import url('https://fonts.googleapis.com/css2?family=Open+Sans:wght@300;400;600;700&display=swap');
        
        * {
            margin: 0;
            padding: 0;
            box-sizing: border-box;
        }

        body {
            font-family: 'Open Sans', 'Roboto', sans-serif;
            background-color: #FAFBFC;
            color: #172B4D;
            line-height: 1.6;
            min-height: 100vh;
            display: flex;
            align-items: center;
            justify-content: center;
            padding: 16px;
        }

        .container {
            background: white;
            max-width: 600px;
            width: 100%;
            padding: 48px;
            border-radius: 12px;
            box-shadow: 0 4px 16px rgba(23, 43, 77, 0.08);
            border: 1px solid #DFE1E6;
        }

        .header {
            text-align: center;
            margin-bottom: 48px;
        }

        .header h1 {
            color: #0052CC;
            font-size: 32px;
            font-weight: 700;
            margin-bottom: 8px;
        }

        .header p {
            color: #5E6C84;
            font-size: 16px;
            font-weight: 400;
        }

        .form-group {
            margin-bottom: 32px;
        }

        .form-group label {
            display: block;
            margin-bottom: 8px;
            font-weight: 600;
            color: #172B4D;
            font-size: 14px;
        }

        .form-group input {
            width: 100%;
            padding: 12px 16px;
            border: 2px solid #DFE1E6;
            border-radius: 8px;
            font-size: 16px;
            font-family: 'Open Sans', sans-serif;
            transition: all 0.2s ease;
            background-color: white;
        }

        .form-group input:focus {
            outline: none;
            border-color: #0052CC;
            box-shadow: 0 0 0 2px rgba(0, 82, 204, 0.2);
        }

        .form-group input.error {
            border-color: #DE350B;
            box-shadow: 0 0 0 2px rgba(222, 53, 11, 0.2);
        }

        .form-group input.success {
            border-color: #00875A;
            box-shadow: 0 0 0 2px rgba(0, 135, 90, 0.2);
        }

        .error-message {
            color: #DE350B;
            font-size: 14px;
            margin-top: 8px;
            display: none;
        }

        .success-message {
            color: #00875A;
            font-size: 14px;
            margin-top: 8px;
            display: none;
        }

        .calculate-btn {
            width: 100%;
            background: linear-gradient(135deg, #0052CC 0%, #0065FF 100%);
            color: white;
            border: none;
            padding: 16px 24px;
            border-radius: 8px;
            font-size: 16px;
            font-weight: 600;
            cursor: pointer;
            transition: all 0.2s ease;
            margin-bottom: 32px;
        }

        .calculate-btn:hover {
            background: linear-gradient(135deg, #003D99 0%, #0052CC 100%);
            transform: translateY(-1px);
            box-shadow: 0 6px 20px rgba(0, 82, 204, 0.3);
        }

        .calculate-btn:active {
            transform: translateY(0);
        }

        .calculate-btn:disabled {
            background: #DFE1E6;
            color: #8993A4;
            cursor: not-allowed;
            transform: none;
            box-shadow: none;
        }

        .result-section {
            background: #E6F3FF;
            border: 2px solid #B3D4FF;
            border-radius: 8px;
            padding: 24px;
            text-align: center;
            display: none;
        }

        .result-section.show {
            display: block;
        }

        .result-section h3 {
            color: #0052CC;
            font-size: 18px;
            font-weight: 600;
            margin-bottom: 16px;
        }

        .iban-display {
            background: white;
            border: 2px solid #00875A;
            border-radius: 8px;
            padding: 16px;
            font-family: 'Courier New', monospace;
            font-size: 20px;
            font-weight: 700;
            color: #172B4D;
            letter-spacing: 2px;
            margin-bottom: 16px;
            word-spacing: 8px;
        }

        .copy-btn {
            background: #00875A;
            color: white;
            border: none;
            padding: 12px 24px;
            border-radius: 6px;
            font-size: 14px;
            font-weight: 600;
            cursor: pointer;
            transition: all 0.2s ease;
        }

        .copy-btn:hover {
            background: #006644;
            transform: translateY(-1px);
        }

        .info-section {
            margin-top: 48px;
            padding-top: 32px;
            border-top: 1px solid #DFE1E6;
        }

        .info-section h4 {
            color: #0052CC;
            font-size: 16px;
            font-weight: 600;
            margin-bottom: 16px;
        }

        .info-section ul {
            list-style: none;
            padding-left: 0;
        }

        .info-section li {
            padding: 8px 0;
            color: #5E6C84;
            font-size: 14px;
        }

        .info-section li:before {
            content: "✓";
            color: #00875A;
            font-weight: bold;
            margin-right: 8px;
        }

        @media (max-width: 768px) {
            .container {
                padding: 32px 24px;
                margin: 16px;
            }

            .header h1 {
                font-size: 28px;
            }

            .iban-display {
                font-size: 16px;
                letter-spacing: 1px;
                word-spacing: 4px;
            }
        }

        .loading {
            display: inline-block;
            width: 20px;
            height: 20px;
            border: 2px solid #ffffff;
            border-radius: 50%;
            border-top-color: transparent;
            animation: spin 1s ease-in-out infinite;
            margin-right: 8px;
        }

        @keyframes spin {
            to { transform: rotate(360deg); }
        }