:root {
            --primary-color: #4361ee;
            --secondary-color: #3a0ca3;
            --success-color: #4cc9f0;
            --danger-color: #f72585;
            --light-color: #f8f9fa;
            --dark-color: #212529;
            --border-color: #dee2e6;
            --shadow: 0 4px 12px rgba(0, 0, 0, 0.1);
        }
        
        * {
            margin: 0;
            padding: 0;
            box-sizing: border-box;
            font-family: 'Segoe UI', Tahoma, Geneva, Verdana, sans-serif;
        }
        
        body {
            background-color: #f5f7ff;
            color: var(--dark-color);
            line-height: 1.6;
            padding: 20px;
            min-height: 100vh;
        }
        
        .container {
            max-width: 1200px;
            margin: 0 auto;
        }
        
        header {
            text-align: center;
            margin-bottom: 40px;
            padding: 20px;
        }
        
        h1 {
            color: var(--secondary-color);
            margin-bottom: 10px;
            font-size: 2.5rem;
        }
        
        .subtitle {
            color: #6c757d;
            font-size: 1.1rem;
            max-width: 700px;
            margin: 0 auto;
        }
        
        .highlight {
            color: var(--primary-color);
            font-weight: 600;
        }
        
        .converter-app {
            display: grid;
            grid-template-columns: 1fr 1fr;
            gap: 30px;
            margin-bottom: 40px;
        }
        
        @media (max-width: 900px) {
            .converter-app {
                grid-template-columns: 1fr;
            }
        }
        
        .upload-section, .preview-section {
            background-color: white;
            border-radius: 12px;
            box-shadow: var(--shadow);
            padding: 30px;
            transition: transform 0.3s ease;
        }
        
        .upload-section:hover, .preview-section:hover {
            transform: translateY(-5px);
        }
        
        .section-title {
            display: flex;
            align-items: center;
            gap: 10px;
            margin-bottom: 25px;
            color: var(--secondary-color);
            font-size: 1.5rem;
        }
        
        .section-title i {
            background-color: #e9ecef;
            width: 40px;
            height: 40px;
            border-radius: 50%;
            display: flex;
            align-items: center;
            justify-content: center;
        }
        
        .upload-area {
            border: 3px dashed var(--border-color);
            border-radius: 10px;
            padding: 50px 20px;
            text-align: center;
            cursor: pointer;
            transition: all 0.3s ease;
            margin-bottom: 20px;
            position: relative;
            overflow: hidden;
        }
        
        .upload-area:hover {
            border-color: var(--primary-color);
            background-color: rgba(67, 97, 238, 0.05);
        }
        
        .upload-area i {
            font-size: 3rem;
            color: var(--primary-color);
            margin-bottom: 15px;
        }
        
        .upload-area h3 {
            margin-bottom: 10px;
            color: var(--dark-color);
        }
        
        .upload-area p {
            color: #6c757d;
            margin-bottom: 20px;
        }
        
        .file-input {
            position: absolute;
            width: 100%;
            height: 100%;
            top: 0;
            left: 0;
            opacity: 0;
            cursor: pointer;
        }
        
        .file-info {
            background-color: #f8f9fa;
            border-radius: 8px;
            padding: 15px;
            margin-top: 20px;
            display: none;
        }
        
        .file-info.active {
            display: block;
        }
        
        .file-details {
            display: flex;
            justify-content: space-between;
            margin-bottom: 10px;
        }
        
        .progress-bar {
            height: 8px;
            background-color: #e9ecef;
            border-radius: 4px;
            overflow: hidden;
            margin-top: 15px;
        }
        
        .progress {
            height: 100%;
            background-color: var(--success-color);
            width: 0%;
            transition: width 0.5s ease;
        }
        
        .convert-btn {
            background-color: var(--primary-color);
            color: white;
            border: none;
            padding: 15px 30px;
            font-size: 1.1rem;
            border-radius: 8px;
            cursor: pointer;
            width: 100%;
            margin-top: 20px;
            transition: background-color 0.3s ease;
            display: flex;
            align-items: center;
            justify-content: center;
            gap: 10px;
        }
        
        .convert-btn:hover {
            background-color: var(--secondary-color);
        }
        
        .convert-btn:disabled {
            background-color: #6c757d;
            cursor: not-allowed;
        }
        
        .preview-container {
            border: 1px solid var(--border-color);
            border-radius: 8px;
            height: 400px;
            overflow-y: auto;
            padding: 15px;
            margin-top: 20px;
            background-color: #f8f9fa;
            position: relative;
        }
        
        .preview-placeholder {
            display: flex;
            flex-direction: column;
            align-items: center;
            justify-content: center;
            height: 100%;
            color: #6c757d;
        }
        
        .preview-placeholder i {
            font-size: 4rem;
            margin-bottom: 20px;
            color: #adb5bd;
        }
        
        .download-section {
            display: flex;
            gap: 15px;
            margin-top: 20px;
        }
        
        .download-btn {
            flex: 1;
            background-color: var(--success-color);
            color: white;
            border: none;
            padding: 15px;
            border-radius: 8px;
            cursor: pointer;
            display: flex;
            align-items: center;
            justify-content: center;
            gap: 10px;
            text-decoration: none;
            transition: background-color 0.3s ease;
        }
        
        .download-btn:hover {
            background-color: #3a8bc0;
        }
        
        .download-btn.disabled {
            background-color: #6c757d;
            cursor: not-allowed;
            pointer-events: none;
        }
        
        .security-features {
            background-color: white;
            border-radius: 12px;
            box-shadow: var(--shadow);
            padding: 30px;
            margin-top: 40px;
        }
        
        .security-grid {
            display: grid;
            grid-template-columns: repeat(auto-fit, minmax(250px, 1fr));
            gap: 20px;
            margin-top: 20px;
        }
        
        .security-item {
            display: flex;
            align-items: flex-start;
            gap: 15px;
        }
        
        .security-icon {
            background-color: rgba(67, 97, 238, 0.1);
            width: 50px;
            height: 50px;
            border-radius: 10px;
            display: flex;
            align-items: center;
            justify-content: center;
            flex-shrink: 0;
        }
        
        .security-icon i {
            color: var(--primary-color);
            font-size: 1.5rem;
        }
        
        .alert {
            padding: 15px;
            border-radius: 8px;
            margin-bottom: 20px;
            display: none;
        }
        
        .alert.success {
            background-color: rgba(76, 201, 240, 0.2);
            border-left: 4px solid var(--success-color);
            display: block;
        }
        
        .alert.error {
            background-color: rgba(247, 37, 133, 0.2);
            border-left: 4px solid var(--danger-color);
            display: block;
        }
        
        .processing-time {
            display: flex;
            justify-content: space-between;
            align-items: center;
            margin-top: 20px;
            padding: 15px;
            background-color: #f8f9fa;
            border-radius: 8px;
        }
        
        .timer {
            font-weight: bold;
            color: var(--primary-color);
            font-size: 1.2rem;
        }
        
        .html-preview {
            font-family: 'Courier New', monospace;
            font-size: 0.9rem;
            white-space: pre-wrap;
            line-height: 1.5;
        }
        
        footer {
            text-align: center;
            margin-top: 50px;
            padding-top: 20px;
            border-top: 1px solid var(--border-color);
            color: #6c757d;
        }
        
        .loading-spinner {
            display: none;
            width: 40px;
            height: 40px;
            border: 4px solid rgba(0, 0, 0, 0.1);
            border-radius: 50%;
            border-top-color: var(--primary-color);
            animation: spin 1s linear infinite;
            margin: 0 auto;
        }
        
        @keyframes spin {
            to { transform: rotate(360deg); }
        }
        
        .converting {
            display: flex;
            flex-direction: column;
            align-items: center;
            justify-content: center;
            height: 100%;
            text-align: center;
        }