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

        body {
            font-family: 'Segoe UI', Tahoma, Geneva, Verdana, sans-serif;
            line-height: 1.6;
            color: #e0e0e0;
            background: linear-gradient(135deg, #1a1a2e 0%, #16213e 50%, #0f3460 100%);
            min-height: 100vh;
            transition: all 0.3s ease;
        }

        /* Light Theme */
        body.light-theme {
            color: #333;
            background: linear-gradient(135deg, #667eea 0%, #764ba2 100%);
        }

        body.light-theme header {
            background: rgba(255, 255, 255, 0.2);
            border-bottom: 1px solid rgba(255, 255, 255, 0.3);
        }

        body.light-theme .feature-card {
            background: rgba(255, 255, 255, 0.2);
            border: 1px solid rgba(255, 255, 255, 0.3);
            color: white;
        }

        body.light-theme .calculator-section {
            background: rgba(255, 255, 255, 0.1);
        }

        body.light-theme .calculator {
            background: rgba(255, 255, 255, 0.95);
            border: 1px solid rgba(255, 255, 255, 0.3);
        }

        body.light-theme .display {
            background: #f8f9fa;
            color: #007bff;
            border: 1px solid #dee2e6;
        }

        body.light-theme .display-expression {
            color: #6c757d;
        }

        body.light-theme .display-result {
            color: #007bff;
        }

        body.light-theme .memory-display {
            background: #e9ecef;
            color: #fd7e14;
            border: 1px solid #dee2e6;
        }

        body.light-theme .btn-number {
            background: #f8f9fa;
            color: #333;
            border: 1px solid #dee2e6;
        }

        body.light-theme .btn-operator {
            background: #007bff;
            border: 1px solid #0056b3;
        }

        body.light-theme .btn-equals {
            background: #28a745;
            border: 1px solid #1e7e34;
        }

        body.light-theme .btn-clear {
            background: #dc3545;
            border: 1px solid #c82333;
        }

        body.light-theme .btn-memory {
            background: #6f42c1;
            border: 1px solid #59359a;
        }

        body.light-theme .history-panel {
            background: rgba(255, 255, 255, 0.95);
            border: 1px solid rgba(255, 255, 255, 0.3);
        }

        body.light-theme .history-title {
            color: #333;
        }

        body.light-theme .history-item {
            border-bottom: 1px solid #dee2e6;
            color: #495057;
        }

        body.light-theme .history-item:hover {
            background: rgba(0, 0, 0, 0.05);
        }

        body.light-theme .clear-history {
            background: #6c757d;
            border: 1px solid #545b62;
        }

        body.light-theme .shortcuts {
            background: rgba(255, 255, 255, 0.2);
            border: 1px solid rgba(255, 255, 255, 0.3);
        }

        .container {
            max-width: 1200px;
            margin: 0 auto;
            padding: 0 20px;
        }

        /* Header */
        header {
            background: rgba(0, 0, 0, 0.3);
            backdrop-filter: blur(10px);
            padding: 1rem 0;
            position: sticky;
            top: 0;
            z-index: 100;
            border-bottom: 1px solid rgba(255, 255, 255, 0.1);
        }

        nav {
            display: flex;
            justify-content: space-between;
            align-items: center;
        }

        .logo {
            font-size: 1.5rem;
            font-weight: bold;
            color: white;
        }

        .nav-center {
            display: flex;
            gap: 2rem;
        }

        .nav-links {
            display: flex;
            gap: 2rem;
        }

        .theme-toggle {
            background: rgba(255, 255, 255, 0.2);
            border: 1px solid rgba(255, 255, 255, 0.3);
            color: white;
            padding: 0.5rem 1rem;
            border-radius: 20px;
            cursor: pointer;
            font-size: 0.9rem;
            transition: all 0.3s;
            display: flex;
            align-items: center;
            gap: 0.5rem;
        }

        .theme-toggle:hover {
            background: rgba(255, 255, 255, 0.3);
        }

        .nav-links a {
            color: white;
            text-decoration: none;
            transition: opacity 0.3s;
        }

        .nav-links a:hover {
            opacity: 0.8;
        }

        /* Home Section */
        .home-section {
            padding: 4rem 0;
            text-align: center;
            color: white;
        }

        .hero-title {
            font-size: 3.5rem;
            font-weight: bold;
            margin-bottom: 1rem;
            text-shadow: 2px 2px 4px rgba(0,0,0,0.3);
        }

        .hero-subtitle {
            font-size: 1.3rem;
            margin-bottom: 2rem;
            opacity: 0.9;
            max-width: 600px;
            margin-left: auto;
            margin-right: auto;
        }

        .features-grid {
            display: grid;
            grid-template-columns: repeat(auto-fit, minmax(300px, 1fr));
            gap: 2rem;
            margin: 3rem 0;
        }

        .feature-card {
            background: rgba(0, 0, 0, 0.3);
            backdrop-filter: blur(10px);
            padding: 2rem;
            border-radius: 15px;
            border: 1px solid rgba(255, 255, 255, 0.1);
            transition: transform 0.3s, box-shadow 0.3s;
        }

        .feature-card:hover {
            transform: translateY(-5px);
            box-shadow: 0 10px 30px rgba(0,0,0,0.2);
        }

        .feature-icon {
            font-size: 3rem;
            margin-bottom: 1rem;
        }

        .feature-title {
            font-size: 1.3rem;
            font-weight: bold;
            margin-bottom: 1rem;
        }

        /* Calculator Section */
        .calculator-section {
            padding: 4rem 0;
            background: rgba(0, 0, 0, 0.2);
        }

        .calculator-container {
            display: grid;
            grid-template-columns: 1fr 300px;
            gap: 3rem;
            max-width: 900px;
            margin: 0 auto;
        }

        .calculator {
            background: rgba(20, 20, 30, 0.95);
            border-radius: 20px;
            padding: 2rem;
            box-shadow: 0 20px 40px rgba(0,0,0,0.3);
            backdrop-filter: blur(10px);
            border: 1px solid rgba(255, 255, 255, 0.1);
        }

        .display {
            background: #0a0a0a;
            color: #00ff88;
            font-family: 'Courier New', monospace;
            font-size: 1.8rem;
            padding: 1.5rem;
            border-radius: 10px;
            margin-bottom: 1.5rem;
            text-align: right;
            min-height: 100px;
            display: flex;
            flex-direction: column;
            justify-content: center;
            word-wrap: break-word;
            overflow-wrap: break-word;
            border: 1px solid #333;
        }

        .display-expression {
            font-size: 1rem;
            color: #888;
            margin-bottom: 0.5rem;
            min-height: 1.2rem;
        }

        .display-result {
            font-size: 2rem;
            color: #00ff88;
        }

        .memory-display {
            background: #1a1a1a;
            color: #ffa500;
            font-size: 0.9rem;
            padding: 0.5rem 1.5rem;
            border-radius: 5px;
            margin-bottom: 1rem;
            text-align: right;
            border: 1px solid #333;
        }

        .button-grid {
            display: grid;
            grid-template-columns: repeat(5, 1fr);
            gap: 10px;
        }

        .btn {
            padding: 1rem;
            border: none;
            border-radius: 10px;
            font-size: 1.2rem;
            font-weight: bold;
            cursor: pointer;
            transition: all 0.2s;
            box-shadow: 0 4px 8px rgba(0,0,0,0.1);
        }

        .btn:hover {
            transform: translateY(-2px);
            box-shadow: 0 6px 12px rgba(0,0,0,0.2);
        }

        .btn:active {
            transform: translateY(0);
            box-shadow: 0 2px 4px rgba(0,0,0,0.2);
        }

        .btn-number {
            background: #2a2a3a;
            color: #e0e0e0;
            border: 1px solid #444;
        }

        .btn-operator {
            background: #0066cc;
            color: white;
            border: 1px solid #0088ff;
        }

        .btn-equals {
            background: #00aa44;
            color: white;
            grid-column: span 2;
            border: 1px solid #00cc55;
        }

        .btn-clear {
            background: #cc3333;
            color: white;
            border: 1px solid #ff4444;
        }

        .btn-memory {
            background: #6633aa;
            color: white;
            font-size: 0.9rem;
            border: 1px solid #7744bb;
        }

        .btn-zero {
            grid-column: span 2;
        }

        /* History Panel */
        .history-panel {
            background: rgba(20, 20, 30, 0.95);
            border-radius: 15px;
            padding: 1.5rem;
            box-shadow: 0 10px 30px rgba(0,0,0,0.3);
            border: 1px solid rgba(255, 255, 255, 0.1);
        }

        .history-title {
            font-size: 1.2rem;
            font-weight: bold;
            margin-bottom: 1rem;
            color: #e0e0e0;
        }

        .history-list {
            max-height: 400px;
            overflow-y: auto;
        }

        .history-item {
            padding: 0.8rem;
            border-bottom: 1px solid #444;
            font-family: 'Courier New', monospace;
            font-size: 0.9rem;
            cursor: pointer;
            transition: background 0.2s;
            color: #ccc;
        }

        .history-item:hover {
            background: rgba(255, 255, 255, 0.1);
        }

        .clear-history {
            width: 100%;
            padding: 0.8rem;
            background: #444;
            color: white;
            border: 1px solid #666;
            border-radius: 8px;
            margin-top: 1rem;
            cursor: pointer;
            transition: background 0.2s;
        }

        .clear-history:hover {
            background: #555;
        }

        /* Keyboard Shortcuts */
        .shortcuts {
            background: rgba(0, 0, 0, 0.3);
            backdrop-filter: blur(10px);
            padding: 2rem;
            border-radius: 15px;
            margin-top: 2rem;
            color: white;
            border: 1px solid rgba(255, 255, 255, 0.1);
        }

        .shortcuts-title {
            font-size: 1.3rem;
            font-weight: bold;
            margin-bottom: 1rem;
        }

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

        .shortcut-item {
            display: flex;
            justify-content: space-between;
            padding: 0.5rem;
            background: rgba(255, 255, 255, 0.1);
            border-radius: 8px;
        }

        /* Footer */
        footer {
            background: rgba(0, 0, 0, 0.8);
            color: white;
            padding: 3rem 0 2rem;
            margin-top: 4rem;
        }

        .footer-content {
            display: grid;
            grid-template-columns: repeat(auto-fit, minmax(300px, 1fr));
            gap: 3rem;
            margin-bottom: 2rem;
        }

        .footer-section h3 {
            font-size: 1.3rem;
            margin-bottom: 1rem;
            color: #00ff88;
        }

        .social-links {
            display: flex;
            gap: 1rem;
            margin-top: 1rem;
        }

        .social-link {
            display: inline-block;
            padding: 0.8rem;
            background: #007bff;
            color: white;
            text-decoration: none;
            border-radius: 8px;
            transition: background 0.3s;
        }

        .social-link:hover {
            background: #0056b3;
        }

        .github-btn {
            display: inline-block;
            padding: 1rem 2rem;
            background: #333;
            color: white;
            text-decoration: none;
            border-radius: 10px;
            font-weight: bold;
            margin-top: 1rem;
            transition: background 0.3s;
        }

        .github-btn:hover {
            background: #555;
        }

        .footer-bottom {
            text-align: center;
            padding-top: 2rem;
            border-top: 1px solid #444;
            opacity: 0.8;
        }

        /* Responsive Design */
        @media (max-width: 1024px) {
            .calculator-container {
                grid-template-columns: 1fr;
                gap: 2rem;
            }

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

        @media (max-width: 768px) {
            .container {
                padding: 0 15px;
            }

            .hero-title {
                font-size: 2.5rem;
            }

            .hero-subtitle {
                font-size: 1.1rem;
            }

            .nav-center {
                display: none;
            }

            .nav-links {
                display: none;
            }

            .home-section {
                padding: 2rem 0;
            }

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

            .calculator {
                padding: 1.5rem;
            }

            .button-grid {
                grid-template-columns: repeat(4, 1fr);
                gap: 8px;
            }

            .btn {
                padding: 0.8rem;
                font-size: 1rem;
            }

            .btn-memory {
                font-size: 0.7rem;
                padding: 0.6rem;
            }

            .display {
                font-size: 1.5rem;
                padding: 1rem;
                min-height: 80px;
            }

            .display-result {
                font-size: 1.8rem;
            }

            .shortcuts-grid {
                grid-template-columns: 1fr;
            }

            .footer-content {
                grid-template-columns: 1fr;
                gap: 2rem;
            }
        }

        @media (max-width: 480px) {
            .hero-title {
                font-size: 2rem;
            }

            .calculator {
                padding: 1rem;
            }

            .btn {
                padding: 0.6rem;
                font-size: 0.9rem;
            }

            .btn-memory {
                font-size: 0.6rem;
                padding: 0.5rem;
            }

            .display {
                font-size: 1.2rem;
                padding: 0.8rem;
            }

            .display-result {
                font-size: 1.5rem;
            }

            .features-grid {
                grid-template-columns: 1fr;
            }

            .feature-card {
                padding: 1.5rem;
            }
        }

        @media (max-width: 360px) {
            .button-grid {
                gap: 6px;
            }

            .btn {
                padding: 0.5rem;
                font-size: 0.8rem;
            }

            .btn-memory {
                font-size: 0.5rem;
            }
        }
    