* {
            margin: 0;
            padding: 0;
            box-sizing: border-box;
            font-family: 'Segoe UI', system-ui, -apple-system, sans-serif;
        }
        
        body {
            background: linear-gradient(135deg, #f5f7fa 0%, #e4edf5 100%);
            display: flex;
            justify-content: center;
            align-items: center;
            min-height: 100vh;
            padding: 20px;
        }
        
        .calculator-container {
            max-width: 400px;
            width: 100%;
            background-color: white;
            border-radius: 24px;
            box-shadow: 0 10px 30px rgba(0, 0, 0, 0.08);
            overflow: hidden;
        }
        
        .calculator-header {
            background: linear-gradient(135deg, #6a11cb 0%, #2575fc 100%);
            color: white;
            padding: 20px 25px;
            display: flex;
            justify-content: space-between;
            align-items: center;
        }
        
        .app-title {
            font-size: 1.5rem;
            font-weight: 600;
        }
        
        .theme-toggle {
            background: rgba(255, 255, 255, 0.2);
            border: none;
            color: white;
            width: 36px;
            height: 36px;
            border-radius: 50%;
            display: flex;
            align-items: center;
            justify-content: center;
            cursor: pointer;
            transition: all 0.3s ease;
        }
        
        .theme-toggle:hover {
            background: rgba(255, 255, 255, 0.3);
        }
        
        .display {
            padding: 25px;
            background-color: #f8f9fa;
            text-align: right;
            border-bottom: 1px solid #eaeaea;
        }
        
        .previous-operand {
            color: #6c757d;
            font-size: 1.1rem;
            min-height: 1.5rem;
            margin-bottom: 8px;
            overflow: hidden;
            text-overflow: ellipsis;
        }
        
        .current-operand {
            color: #212529;
            font-size: 2.8rem;
            font-weight: 300;
            overflow: hidden;
            text-overflow: ellipsis;
        }
        
        .buttons-grid {
            display: grid;
            grid-template-columns: repeat(4, 1fr);
            grid-gap: 1px;
            background-color: #eaeaea;
        }
        
        button {
            background-color: white;
            border: none;
            color: #333;
            cursor: pointer;
            font-size: 1.4rem;
            font-weight: 500;
            padding: 20px 0;
            transition: all 0.2s ease;
            outline: none;
            position: relative;
            overflow: hidden;
        }
        
        button::after {
            content: '';
            position: absolute;
            top: 50%;
            left: 50%;
            width: 5px;
            height: 5px;
            background: rgba(0, 0, 0, 0.1);
            opacity: 0;
            border-radius: 100%;
            transform: scale(1, 1) translate(-50%);
            transform-origin: 50% 50%;
        }
        
        button:focus::after {
            animation: ripple 1s ease-out;
        }
        
        @keyframes ripple {
            0% {
                transform: scale(0, 0);
                opacity: 0.5;
            }
            100% {
                transform: scale(100, 100);
                opacity: 0;
            }
        }
        
        button:hover {
            background-color: #f8f9fa;
        }
        
        button:active {
            background-color: #e9ecef;
        }
        
        .operation {
            color: #2575fc;
            font-weight: 500;
        }
        
        .equals {
            background: linear-gradient(135deg, #6a11cb 0%, #2575fc 100%);
            color: white;
        }
        
        .equals:hover {
            background: linear-gradient(135deg, #5a0db5 0%, #1c68e6 100%);
        }
        
        .clear, .delete {
            color: #e74c3c;
        }
        
        .span-two {
            grid-column: span 2;
        }
        
        .calculator-footer {
            padding: 15px 25px;
            background-color: #f8f9fa;
            border-top: 1px solid #eaeaea;
            display: flex;
            justify-content: space-between;
            align-items: center;
            color: #6c757d;
            font-size: 0.9rem;
        }
        
        .memory-indicator {
            display: flex;
            align-items: center;
            gap: 5px;
        }
        
        .memory-indicator.active {
            color: #2575fc;
        }
        
        @media (max-width: 480px) {
            .calculator-container {
                max-width: 100%;
            }
            
            button {
                padding: 18px 0;
                font-size: 1.3rem;
            }
            
            .current-operand {
                font-size: 2.5rem;
            }
        }
        
        /* Dark mode styles */
        body.dark-mode {
            background: linear-gradient(135deg, #232526 0%, #414345 100%);
        }
        
        body.dark-mode .calculator-container {
            background-color: #2d3748;
            color: #e2e8f0;
        }
        
        body.dark-mode .display {
            background-color: #1a202c;
            border-bottom-color: #4a5568;
        }
        
        body.dark-mode .current-operand {
            color: #f7fafc;
        }
        
        body.dark-mode .previous-operand {
            color: #a0aec0;
        }
        
        body.dark-mode .buttons-grid {
            background-color: #4a5568;
        }
        
        body.dark-mode button {
            background-color: #2d3748;
            color: #e2e8f0;
        }
        
        body.dark-mode button:hover {
            background-color: #4a5568;
        }
        
        body.dark-mode button:active {
            background-color: #1a202c;
        }
        
        body.dark-mode .calculator-footer {
            background-color: #1a202c;
            border-top-color: #4a5568;
            color: #a0aec0;
        }