:root {
            --primary: #1a73e8;
            --secondary: #0f9d58;
            --accent: #673ab7;
            --danger: #ea4335;
            --warning: #fbbc04;
            --dark: #202124;
            --light: #f8f9fa;
            --gray: #5f6368;
            --shadow: 0 4px 12px rgba(0, 0, 0, 0.15);
            --radius: 12px;
            --transition: all 0.3s ease;
        }

        * {
            margin: 0;
            padding: 0;
            box-sizing: border-box;
            font-family: 'Segoe UI', Arial, sans-serif;
        }

        body {
            background: linear-gradient(135deg, #f5f7fa 0%, #e4e8f0 100%);
            min-height: 100vh;
            display: flex;
            justify-content: center;
            align-items: center;
            padding: 20px;
            color: var(--dark);
        }

        .container {
            width: 100%;
            max-width: 1200px;
            background: white;
            border-radius: 20px;
            box-shadow: 0 20px 60px rgba(0, 0, 0, 0.1);
            overflow: hidden;
        }

        .header {
            background: linear-gradient(135deg, var(--primary), var(--accent));
            color: white;
            padding: 40px;
            text-align: center;
            position: relative;
            overflow: hidden;
        }

        .header-content {
            position: relative;
            z-index: 1;
        }

        .header h1 {
            font-size: 2.5rem;
            margin-bottom: 15px;
            display: flex;
            align-items: center;
            justify-content: center;
            gap: 20px;
            font-weight: 700;
        }

        .header h1 i {
            font-size: 2.8rem;
        }

        .subtitle {
            font-size: 1.1rem;
            opacity: 0.9;
            margin-bottom: 10px;
        }

        .file-size-badge {
            display: inline-flex;
            align-items: center;
            gap: 10px;
            background: rgba(255, 255, 255, 0.2);
            border: 2px solid rgba(255, 255, 255, 0.3);
            border-radius: 50px;
            padding: 12px 25px;
            margin-top: 20px;
            font-weight: 600;
        }

        .main-content {
            padding: 40px;
            display: grid;
            grid-template-columns: 1fr 1fr;
            gap: 40px;
        }

        @media (max-width: 900px) {
            .main-content {
                grid-template-columns: 1fr;
            }
        }

        .upload-section {
            background: var(--light);
            border-radius: var(--radius);
            padding: 30px;
            box-shadow: var(--shadow);
            border: 2px dashed var(--primary);
            transition: var(--transition);
        }

        .upload-section.dragover {
            border-color: var(--secondary);
            background: rgba(15, 157, 88, 0.05);
        }

        .upload-icon {
            text-align: center;
            margin-bottom: 25px;
        }

        .upload-icon i {
            font-size: 5rem;
            color: var(--primary);
            margin-bottom: 15px;
        }

        .upload-text {
            text-align: center;
            margin-bottom: 25px;
        }

        .upload-text h2 {
            color: var(--dark);
            margin-bottom: 10px;
            font-size: 1.5rem;
        }

        .upload-text p {
            color: var(--gray);
            font-size: 0.95rem;
        }

        .file-input-wrapper {
            text-align: center;
        }

        .file-input {
            display: none;
        }

        .browse-btn {
            background: linear-gradient(135deg, var(--primary), #4285f4);
            color: white;
            border: none;
            padding: 18px 40px;
            border-radius: 50px;
            font-size: 1.1rem;
            font-weight: 600;
            cursor: pointer;
            transition: var(--transition);
            display: inline-flex;
            align-items: center;
            gap: 12px;
        }

        .browse-btn:hover {
            transform: translateY(-3px);
            box-shadow: 0 10px 25px rgba(26, 115, 232, 0.4);
        }

        .security-note {
            text-align: center;
            margin-top: 25px;
            padding: 15px;
            background: rgba(15, 157, 88, 0.1);
            border-radius: var(--radius);
            color: var(--secondary);
            font-size: 0.9rem;
        }

        .security-note i {
            margin-right: 8px;
        }

        .conversion-section {
            background: white;
            border-radius: var(--radius);
            padding: 30px;
            box-shadow: var(--shadow);
            border: 1px solid #e0e0e0;
        }

        .file-info {
            background: linear-gradient(135deg, #f8f9fa, #e9ecef);
            border-radius: var(--radius);
            padding: 25px;
            margin-bottom: 25px;
            display: none;
        }

        .file-info.show {
            display: block;
        }

        .file-details {
            display: flex;
            justify-content: space-between;
            align-items: center;
            margin-bottom: 20px;
            flex-wrap: wrap;
            gap: 15px;
        }

        .file-name {
            font-weight: 600;
            font-size: 1.1rem;
            color: var(--dark);
            word-break: break-all;
        }

        .file-size {
            background: var(--primary);
            color: white;
            padding: 8px 16px;
            border-radius: 20px;
            font-weight: 600;
            font-size: 0.9rem;
        }

        .progress-container {
            margin-bottom: 25px;
        }

        .progress-header {
            display: flex;
            justify-content: space-between;
            margin-bottom: 10px;
            font-size: 0.9rem;
            color: var(--gray);
        }

        .progress-bar {
            height: 10px;
            background: #e0e0e0;
            border-radius: 5px;
            overflow: hidden;
        }

        .progress-fill {
            height: 100%;
            background: linear-gradient(90deg, var(--primary), var(--secondary));
            width: 0%;
            transition: width 0.4s ease;
            border-radius: 5px;
        }

        .progress-stats {
            display: grid;
            grid-template-columns: repeat(3, 1fr);
            gap: 15px;
            margin-top: 20px;
        }

        .stat-card {
            background: white;
            padding: 15px;
            border-radius: 8px;
            text-align: center;
            border: 1px solid #e0e0e0;
        }

        .stat-card i {
            font-size: 1.5rem;
            margin-bottom: 10px;
            color: var(--primary);
        }

        .stat-value {
            font-size: 1.2rem;
            font-weight: 600;
            color: var(--dark);
            margin-bottom: 5px;
        }

        .stat-label {
            font-size: 0.85rem;
            color: var(--gray);
        }

        .actions {
            display: flex;
            gap: 15px;
            margin-top: 30px;
        }

        .action-btn {
            flex: 1;
            padding: 18px;
            border: none;
            border-radius: var(--radius);
            font-size: 1rem;
            font-weight: 600;
            cursor: pointer;
            transition: var(--transition);
            display: flex;
            align-items: center;
            justify-content: center;
            gap: 12px;
            min-height: 60px;
        }

        .convert-btn {
            background: linear-gradient(135deg, var(--secondary), #0a8c4a);
            color: white;
        }

        .convert-btn:hover:not(:disabled) {
            transform: translateY(-3px);
            box-shadow: 0 10px 25px rgba(15, 157, 88, 0.4);
        }

        .convert-btn:disabled {
            opacity: 0.6;
            cursor: not-allowed;
        }

        .download-btn {
            background: linear-gradient(135deg, var(--danger), #d32f2f);
            color: white;
            display: none;
        }

        .download-btn:hover {
            transform: translateY(-3px);
            box-shadow: 0 10px 25px rgba(234, 67, 53, 0.4);
        }

        .download-btn.show {
            display: flex;
        }

        .result-section {
            margin-top: 30px;
            padding: 25px;
            background: linear-gradient(135deg, #e8f5e9, #c8e6c9);
            border-radius: var(--radius);
            border-left: 5px solid var(--secondary);
            display: none;
        }

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

        .performance-info {
            background: linear-gradient(135deg, #fff3e0, #ffecb3);
            border-radius: var(--radius);
            padding: 25px;
            margin-top: 30px;
            border-left: 5px solid var(--warning);
        }

        .info-title {
            display: flex;
            align-items: center;
            gap: 10px;
            margin-bottom: 15px;
            color: var(--dark);
        }

        .info-title i {
            color: var(--warning);
        }

        .features-grid {
            display: grid;
            grid-template-columns: repeat(auto-fit, minmax(200px, 1fr));
            gap: 15px;
            margin-top: 20px;
        }

        .feature {
            background: white;
            padding: 15px;
            border-radius: 8px;
            font-size: 0.9rem;
            display: flex;
            align-items: center;
            gap: 10px;
            border: 1px solid #e0e0e0;
        }

        .feature i {
            color: var(--secondary);
        }

        .data-preview {
            background: white;
            border-radius: var(--radius);
            padding: 20px;
            margin-top: 25px;
            border: 1px solid #e0e0e0;
            max-height: 300px;
            overflow-y: auto;
            display: none;
        }

        .data-preview.show {
            display: block;
        }

        .preview-table {
            width: 100%;
            border-collapse: collapse;
            font-size: 0.85rem;
        }

        .preview-table th {
            background: var(--primary);
            color: white;
            padding: 12px;
            text-align: left;
        }

        .preview-table td {
            padding: 10px;
            border-bottom: 1px solid #e0e0e0;
        }

        .preview-table tr:hover {
            background: #f5f5f5;
        }

        .footer {
            text-align: center;
            padding: 25px;
            background: var(--light);
            color: var(--gray);
            font-size: 0.9rem;
            border-top: 1px solid #e0e0e0;
        }

        .spinner {
            width: 24px;
            height: 24px;
            border: 3px solid rgba(255, 255, 255, 0.3);
            border-radius: 50%;
            border-top-color: white;
            animation: spin 1s linear infinite;
            display: inline-block;
        }

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

        .toast {
            position: fixed;
            bottom: 20px;
            right: 20px;
            background: var(--secondary);
            color: white;
            padding: 15px 25px;
            border-radius: var(--radius);
            box-shadow: 0 10px 30px rgba(0,0,0,0.2);
            z-index: 1000;
            font-weight: 600;
            display: flex;
            align-items: center;
            gap: 10px;
            opacity: 0;
            transform: translateY(20px);
            transition: all 0.3s;
        }

        .toast.show {
            opacity: 1;
            transform: translateY(0);
        }

        .toast.error {
            background: var(--danger);
        }