* {
            margin: 0;
            padding: 0;
            box-sizing: border-box;
        }

        :root {
            --primary-color: #3B82F6;
            --primary-dark: #2563EB;
            --primary-light: #60A5FA;
            --success-color: #10B981;
            --error-color: #EF4444;
            --text-dark: #111827;
            --text-medium: #374151;
            --text-light: #6B7280;
            --bg-white: #FFFFFF;
            --bg-light: #F9FAFB;
            --bg-lighter: #F3F4F6;
            --border-color: #E5E7EB;
            --border-dark: #D1D5DB;
            --shadow-sm: 0 1px 2px 0 rgba(0, 0, 0, 0.05);
            --shadow-md: 0 4px 6px -1px rgba(0, 0, 0, 0.1);
            --shadow-lg: 0 10px 15px -3px rgba(0, 0, 0, 0.1);
            --shadow-xl: 0 20px 25px -5px rgba(0, 0, 0, 0.1);
            --radius-sm: 0.375rem;
            --radius-md: 0.5rem;
            --radius-lg: 0.75rem;
        }

        body {
            font-family: 'Inter', -apple-system, BlinkMacSystemFont, 'Segoe UI', sans-serif;
            background-color: var(--bg-white);
            color: var(--text-medium);
            line-height: 1.7;
            overflow-x: hidden;
        }

        /* Header Styles */
        header {
            background-color: var(--bg-white);
            border-bottom: 1px solid var(--border-color);
            position: sticky;
            top: 0;
            z-index: 1000;
            box-shadow: var(--shadow-sm);
        }

        .header-container {
            max-width: 1280px;
            margin: 0 auto;
            padding: 1rem 1.5rem;
            display: flex;
            justify-content: space-between;
            align-items: center;
        }

        .logo {
            font-size: 1.5rem;
            font-weight: 700;
            color: var(--text-dark);
            text-decoration: none;
            display: flex;
            align-items: center;
            gap: 0.5rem;
        }

        .logo-icon {
            width: 32px;
            height: 32px;
            background: linear-gradient(135deg, var(--primary-color), var(--primary-light));
            border-radius: var(--radius-md);
            display: flex;
            align-items: center;
            justify-content: center;
            color: white;
            font-weight: 700;
            font-size: 1.25rem;
        }

        .nav-link {
            color: var(--text-medium);
            text-decoration: none;
            font-weight: 500;
            padding: 0.5rem 1rem;
            border-radius: var(--radius-md);
            transition: all 0.2s ease;
        }

        .nav-link:hover {
            color: var(--primary-color);
            background-color: var(--bg-lighter);
        }

        /* Hero Section */
        .hero {
            background: linear-gradient(135deg, #EFF6FF 0%, #DBEAFE 100%);
            padding: 3rem 1.5rem 2rem;
        }

        .hero-container {
            max-width: 1280px;
            margin: 0 auto;
            text-align: center;
        }

        .hero h1 {
            font-size: 2.5rem;
            font-weight: 700;
            color: var(--text-dark);
            margin-bottom: 1rem;
            line-height: 1.2;
        }

        .hero p {
            font-size: 1.125rem;
            color: var(--text-medium);
            max-width: 600px;
            margin: 0 auto 2rem;
        }

        /* Calculator Section */
        .calculator-section {
            max-width: 900px;
            margin: -2rem auto 0;
            padding: 0 1.5rem 3rem;
        }

        .calculator-card {
            background-color: var(--bg-white);
            border-radius: var(--radius-lg);
            box-shadow: var(--shadow-xl);
            padding: 2rem;
            border: 1px solid var(--border-color);
        }

        .input-group {
            margin-bottom: 1.5rem;
        }

        label {
            display: block;
            font-weight: 600;
            color: var(--text-dark);
            margin-bottom: 0.5rem;
            font-size: 0.875rem;
            text-transform: uppercase;
            letter-spacing: 0.05em;
        }

        .input-wrapper {
            position: relative;
        }

        textarea {
            width: 100%;
            padding: 1rem;
            border: 2px solid var(--border-color);
            border-radius: var(--radius-md);
            font-family: 'JetBrains Mono', monospace;
            font-size: 1rem;
            resize: vertical;
            min-height: 100px;
            transition: all 0.2s ease;
        }

        textarea:focus {
            outline: none;
            border-color: var(--primary-color);
            box-shadow: 0 0 0 3px rgba(59, 130, 246, 0.1);
        }

        .hint-text {
            font-size: 0.875rem;
            color: var(--text-light);
            margin-top: 0.5rem;
        }

        .operation-buttons {
            display: grid;
            grid-template-columns: repeat(auto-fit, minmax(140px, 1fr));
            gap: 0.75rem;
            margin-bottom: 1.5rem;
        }

        .btn {
            padding: 0.875rem 1.5rem;
            border: none;
            border-radius: var(--radius-md);
            font-weight: 600;
            font-size: 0.9375rem;
            cursor: pointer;
            transition: all 0.2s ease;
            text-align: center;
            display: inline-flex;
            align-items: center;
            justify-content: center;
            gap: 0.5rem;
        }

        .btn-primary {
            background-color: var(--primary-color);
            color: white;
            box-shadow: var(--shadow-sm);
        }

        .btn-primary:hover {
            background-color: var(--primary-dark);
            box-shadow: var(--shadow-md);
            transform: translateY(-1px);
        }

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

        .btn-secondary {
            background-color: var(--bg-lighter);
            color: var(--text-dark);
            border: 1px solid var(--border-color);
        }

        .btn-secondary:hover {
            background-color: var(--border-color);
        }

        .btn-outline {
            background-color: transparent;
            color: var(--text-medium);
            border: 1px solid var(--border-dark);
        }

        .btn-outline:hover {
            background-color: var(--bg-lighter);
            border-color: var(--text-medium);
        }

        .action-buttons {
            display: flex;
            gap: 0.75rem;
            flex-wrap: wrap;
        }

        .btn-lg {
            padding: 1rem 2rem;
            font-size: 1rem;
            flex: 1;
            min-width: 140px;
        }

        /* Results Section */
        .results-section {
            margin-top: 2rem;
            display: none;
        }

        .results-section.active {
            display: block;
            animation: fadeIn 0.3s ease;
        }

        @keyframes fadeIn {
            from {
                opacity: 0;
                transform: translateY(10px);
            }
            to {
                opacity: 1;
                transform: translateY(0);
            }
        }

        .result-card {
            background-color: var(--bg-light);
            border-radius: var(--radius-md);
            padding: 1.5rem;
            border-left: 4px solid var(--primary-color);
            margin-bottom: 1rem;
        }

        .result-label {
            font-size: 0.875rem;
            font-weight: 600;
            color: var(--text-light);
            text-transform: uppercase;
            letter-spacing: 0.05em;
            margin-bottom: 0.5rem;
        }

        .result-value {
            font-family: 'JetBrains Mono', monospace;
            font-size: 1.25rem;
            font-weight: 500;
            color: var(--text-dark);
            word-wrap: break-word;
        }

        .steps-container {
            background-color: var(--bg-white);
            border-radius: var(--radius-md);
            border: 1px solid var(--border-color);
            padding: 1.5rem;
        }

        .steps-header {
            font-size: 1.125rem;
            font-weight: 600;
            color: var(--text-dark);
            margin-bottom: 1rem;
            display: flex;
            align-items: center;
            gap: 0.5rem;
        }

        .step {
            padding: 1rem;
            border-left: 3px solid var(--border-color);
            margin-bottom: 0.75rem;
            position: relative;
            padding-left: 2.5rem;
        }

        .step::before {
            content: attr(data-step);
            position: absolute;
            left: -0.75rem;
            top: 1rem;
            background-color: var(--primary-color);
            color: white;
            width: 1.5rem;
            height: 1.5rem;
            border-radius: 50%;
            display: flex;
            align-items: center;
            justify-content: center;
            font-size: 0.75rem;
            font-weight: 700;
        }

        .step-description {
            color: var(--text-medium);
            font-size: 0.9375rem;
            margin-bottom: 0.5rem;
        }

        .step-math {
            font-family: 'JetBrains Mono', monospace;
            background-color: var(--bg-lighter);
            padding: 0.75rem;
            border-radius: var(--radius-sm);
            font-size: 0.9375rem;
            color: var(--text-dark);
            overflow-x: auto;
        }

        /* Error Message */
        .error-message {
            background-color: #FEE2E2;
            border-left: 4px solid var(--error-color);
            color: #991B1B;
            padding: 1rem;
            border-radius: var(--radius-md);
            margin-top: 1rem;
            display: none;
        }

        .error-message.active {
            display: block;
            animation: fadeIn 0.3s ease;
        }

        /* Examples Section */
        .examples-section {
            max-width: 900px;
            margin: 3rem auto;
            padding: 0 1.5rem;
        }

        .section-title {
            font-size: 1.875rem;
            font-weight: 700;
            color: var(--text-dark);
            margin-bottom: 1.5rem;
            text-align: center;
        }

        .examples-grid {
            display: grid;
            grid-template-columns: repeat(auto-fit, minmax(250px, 1fr));
            gap: 1rem;
        }

        .example-card {
            background-color: var(--bg-white);
            border: 1px solid var(--border-color);
            border-radius: var(--radius-md);
            padding: 1.25rem;
            cursor: pointer;
            transition: all 0.2s ease;
        }

        .example-card:hover {
            border-color: var(--primary-color);
            box-shadow: var(--shadow-md);
            transform: translateY(-2px);
        }

        .example-title {
            font-weight: 600;
            color: var(--text-dark);
            margin-bottom: 0.5rem;
            font-size: 0.9375rem;
        }

        .example-math {
            font-family: 'JetBrains Mono', monospace;
            color: var(--primary-color);
            font-size: 0.875rem;
        }

        /* Article Section */
        .article-section {
            max-width: 900px;
            margin: 4rem auto;
            padding: 0 1.5rem;
        }

        .article-content {
            background-color: var(--bg-white);
            border-radius: var(--radius-lg);
            padding: 3rem 2.5rem;
            box-shadow: var(--shadow-md);
            border: 1px solid var(--border-color);
        }

        .article-content h2 {
            font-size: 1.75rem;
            font-weight: 700;
            color: var(--text-dark);
            margin-top: 2.5rem;
            margin-bottom: 1rem;
            line-height: 1.3;
        }

        .article-content h2:first-child {
            margin-top: 0;
        }

        .article-content h3 {
            font-size: 1.375rem;
            font-weight: 600;
            color: var(--text-dark);
            margin-top: 2rem;
            margin-bottom: 0.75rem;
        }

        .article-content p {
            margin-bottom: 1.25rem;
            font-size: 1.0625rem;
            line-height: 1.8;
        }

        .article-content ul, .article-content ol {
            margin-bottom: 1.25rem;
            padding-left: 1.75rem;
        }

        .article-content li {
            margin-bottom: 0.5rem;
            font-size: 1.0625rem;
            line-height: 1.7;
        }

        .article-content strong {
            color: var(--text-dark);
            font-weight: 600;
        }

        .keyword-highlight {
            background: linear-gradient(120deg, #EFF6FF 0%, #DBEAFE 100%);
            padding: 0.125rem 0.25rem;
            border-radius: 0.25rem;
        }

        /* Footer */
        footer {
            background-color: var(--bg-lighter);
            border-top: 1px solid var(--border-color);
            padding: 3rem 1.5rem 2rem;
            margin-top: 4rem;
        }

        .footer-container {
            max-width: 1280px;
            margin: 0 auto;
        }

        .footer-grid {
            display: grid;
            grid-template-columns: repeat(auto-fit, minmax(200px, 1fr));
            gap: 2rem;
            margin-bottom: 2rem;
        }

        .footer-section h3 {
            font-size: 1rem;
            font-weight: 600;
            color: var(--text-dark);
            margin-bottom: 1rem;
        }

        .footer-links {
            list-style: none;
        }

        .footer-links li {
            margin-bottom: 0.5rem;
        }

        .footer-links a {
            color: var(--text-medium);
            text-decoration: none;
            transition: color 0.2s ease;
        }

        .footer-links a:hover {
            color: var(--primary-color);
        }

        .footer-bottom {
            text-align: center;
            padding-top: 2rem;
            border-top: 1px solid var(--border-color);
            color: var(--text-light);
            font-size: 0.875rem;
        }

        /* Responsive Design */
        @media (max-width: 768px) {
            .hero h1 {
                font-size: 1.875rem;
            }

            .hero p {
                font-size: 1rem;
            }

            .calculator-card {
                padding: 1.5rem;
            }

            .operation-buttons {
                grid-template-columns: repeat(2, 1fr);
            }

            .action-buttons {
                flex-direction: column;
            }

            .btn-lg {
                width: 100%;
            }

            .article-content {
                padding: 2rem 1.5rem;
            }

            .article-content h2 {
                font-size: 1.5rem;
            }

            .footer-grid {
                grid-template-columns: 1fr;
                gap: 1.5rem;
            }
        }

        @media (max-width: 480px) {
            .header-container {
                padding: 0.75rem 1rem;
            }

            .logo {
                font-size: 1.25rem;
            }

            .hero {
                padding: 2rem 1rem 1.5rem;
            }

            .calculator-section {
                padding: 0 1rem 2rem;
            }

            .operation-buttons {
                grid-template-columns: 1fr;
            }

            .article-content {
                padding: 1.5rem 1rem;
            }
        }

        /* Loading Animation */
        .loading {
            display: inline-block;
            width: 16px;
            height: 16px;
            border: 2px solid rgba(255, 255, 255, 0.3);
            border-radius: 50%;
            border-top-color: white;
            animation: spin 0.8s linear infinite;
        }

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