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

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

/* Calculator Container */
.calculator-container {
    width: 100%;
    max-width: 400px;
    margin: 0 auto;
}

.calculator {
    background-color: #1a1a1a;
    border-radius: 20px;
    padding: 25px;
    box-shadow: 0 20px 60px rgba(0, 0, 0, 0.3);
}

/* Display Screen */
.display {
    background-color: #0a0a0a;
    border-radius: 10px;
    padding: 20px;
    margin-bottom: 20px;
    min-height: 100px;
    display: flex;
    align-items: center;
    justify-content: flex-end;
    overflow: hidden;
}

.display-content {
    color: #ffffff;
    font-size: 2.5rem;
    font-weight: 300;
    word-wrap: break-word;
    word-break: break-all;
    text-align: right;
    width: 100%;
    transition: font-size 0.2s;
}

/* Button Grid */
.buttons {
    display: grid;
    grid-template-columns: repeat(4, 1fr);
    gap: 15px;
}

/* Button Base Styles */
.btn {
    background-color: #2d2d2d;
    color: #ffffff;
    border: none;
    border-radius: 10px;
    font-size: 1.5rem;
    font-weight: 500;
    padding: 20px;
    cursor: pointer;
    transition: all 0.2s ease;
    box-shadow: 0 4px 6px rgba(0, 0, 0, 0.2);
    user-select: none;
}

/* Button Hover Effect */
.btn:hover {
    background-color: #3d3d3d;
    transform: translateY(-2px);
    box-shadow: 0 6px 12px rgba(0, 0, 0, 0.3);
}

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

/* Number Buttons */
.btn.number {
    background-color: #3d3d3d;
}

.btn.number:hover {
    background-color: #4d4d4d;
}

/* Operator Buttons */
.btn.operator {
    background-color: #ff9500;
    color: #ffffff;
}

.btn.operator:hover {
    background-color: #ffaa33;
}

.btn.operator.active {
    background-color: #ffffff;
    color: #ff9500;
}

/* Equals Button */
.btn.equals {
    background-color: #ff9500;
    color: #ffffff;
    grid-row: span 2;
}

.btn.equals:hover {
    background-color: #ffaa33;
}

/* Zero Button - Span 2 columns */
.btn.zero {
    grid-column: span 1;
}

/* Responsive Design */
@media (max-width: 480px) {
    .calculator {
        padding: 20px;
    }
    
    .display {
        padding: 15px;
        min-height: 80px;
    }
    
    .display-content {
        font-size: 2rem;
    }
    
    .btn {
        font-size: 1.3rem;
        padding: 18px;
    }
    
    .buttons {
        gap: 12px;
    }
}

@media (max-width: 360px) {
    .display-content {
        font-size: 1.5rem;
    }
    
    .btn {
        font-size: 1.1rem;
        padding: 15px;
    }
    
    .buttons {
        gap: 10px;
    }
}

/* Animation for display updates */
.display-content.updated {
    animation: pulse 0.2s ease;
}

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