/* CSS Reset and Base Styles */
* {
    margin: 0;
    padding: 0;
    box-sizing: border-box;
}

body {
    font-family: -apple-system, BlinkMacSystemFont, 'Segoe UI', Roboto, Oxygen, Ubuntu, Cantarell, sans-serif;
    background: linear-gradient(135deg, #667eea 0%, #764ba2 100%);
    min-height: 100vh;
    display: flex;
    justify-content: center;
    align-items: center;
    padding: 20px;
}

.container {
    width: 100%;
    max-width: 400px;
}

h1 {
    text-align: center;
    color: #ffffff;
    margin-bottom: 30px;
    font-size: 2rem;
    text-shadow: 2px 2px 4px rgba(0, 0, 0, 0.2);
}

.calculator {
    background: #ffffff;
    border-radius: 20px;
    padding: 30px;
    box-shadow: 0 20px 60px rgba(0, 0, 0, 0.3);
}

/* Input Styles */
.input-group {
    display: flex;
    gap: 15px;
    margin-bottom: 25px;
}

#num1,
#num2 {
    flex: 1;
    padding: 15px;
    font-size: 1.1rem;
    border: 2px solid #e0e0e0;
    border-radius: 10px;
    transition: all 0.3s ease;
    background: #f8f9fa;
}

#num1:focus,
#num2:focus {
    outline: none;
    border-color: #667eea;
    background: #ffffff;
    box-shadow: 0 0 0 3px rgba(102, 126, 234, 0.1);
}

/* Button Styles */
.button-group {
    display: grid;
    grid-template-columns: repeat(4, 1fr);
    gap: 10px;
    margin-bottom: 25px;
}

.btn {
    padding: 20px;
    font-size: 1.5rem;
    font-weight: bold;
    border: none;
    border-radius: 10px;
    cursor: pointer;
    transition: all 0.3s ease;
    position: relative;
    overflow: hidden;
}

.btn-operation {
    background: linear-gradient(135deg, #667eea 0%, #764ba2 100%);
    color: #ffffff;
}

.btn-operation:hover {
    transform: translateY(-2px);
    box-shadow: 0 5px 15px rgba(102, 126, 234, 0.4);
}

.btn-operation:active,
.btn-operation.active {
    transform: translateY(0);
    box-shadow: 0 2px 5px rgba(102, 126, 234, 0.4);
}

/* Result Display */
.result-container {
    margin-bottom: 20px;
}

.result-container label {
    display: block;
    margin-bottom: 10px;
    color: #555;
    font-weight: 600;
    font-size: 0.9rem;
    text-transform: uppercase;
    letter-spacing: 1px;
}

#calc-result {
    padding: 20px;
    background: #f8f9fa;
    border-radius: 10px;
    font-size: 1.8rem;
    font-weight: bold;
    text-align: right;
    color: #333;
    min-height: 60px;
    display: flex;
    align-items: center;
    justify-content: flex-end;
    border: 2px solid #e0e0e0;
    transition: all 0.3s ease;
}

#calc-result.error {
    color: #e74c3c;
    background: #ffe6e6;
    border-color: #e74c3c;
    font-size: 1.2rem;
}

#calc-result.animate {
    animation: pulse 0.3s ease;
}

@keyframes pulse {
    0% {
        transform: scale(1);
    }
    50% {
        transform: scale(1.05);
    }
    100% {
        transform: scale(1);
    }
}

/* Instructions */
.instructions {
    text-align: center;
    color: #666;
    font-size: 0.9rem;
    padding: 10px;
    background: #f8f9fa;
    border-radius: 10px;
}

.instructions p {
    margin: 0;
}

/* Responsive Design */
@media (max-width: 480px) {
    h1 {
        font-size: 1.5rem;
    }
    
    .calculator {
        padding: 20px;
    }
    
    .input-group {
        flex-direction: column;
        gap: 10px;
    }
    
    .button-group {
        grid-template-columns: repeat(2, 1fr);
    }
    
    .btn {
        padding: 15px;
        font-size: 1.2rem;
    }
    
    #calc-result {
        font-size: 1.5rem;
        padding: 15px;
    }
}

/* Accessibility */
@media (prefers-reduced-motion: reduce) {
    * {
        animation: none !important;
        transition: none !important;
    }
}

/* Dark mode support */
@media (prefers-color-scheme: dark) {
    body {
        background: linear-gradient(135deg, #4a5568 0%, #2d3748 100%);
    }
    
    .calculator {
        background: #2d3748;
        color: #e2e8f0;
    }
    
    #num1,
    #num2,
    #calc-result {
        background: #1a202c;
        color: #e2e8f0;
        border-color: #4a5568;
    }
    
    .result-container label {
        color: #a0aec0;
    }
    
    .instructions {
        background: #1a202c;
        color: #a0aec0;
    }
}