body {
    font-family: 'Segoe UI', Tahoma, Geneva, Verdana, sans-serif;
    transition: background-color 0.3s, color 0.3s;
}

.calculator {
    max-width: 400px;
    margin: 0 auto;
    border-radius: 10px;
    box-shadow: 0 4px 12px rgba(0, 0, 0, 0.1);
    overflow: hidden;
}

.display {
    padding: 20px;
    text-align: right;
    background-color: #f8f9fa;
    border-bottom: 1px solid #dee2e6;
}

.display .previous-operation {
    min-height: 24px;
    font-size: 1rem;
    color: #6c757d;
}

.display .current-value {
    font-size: 2rem;
    font-weight: bold;
}

.keypad {
    display: grid;
    grid-template-columns: repeat(4, 1fr);
    gap: 1px;
    background-color: #dee2e6;
}

.keypad button {
    border: none;
    padding: 20px;
    font-size: 1.2rem;
    background-color: white;
    cursor: pointer;
    transition: background-color 0.2s;
}

.keypad button:hover {
    background-color: #e9ecef;
}

.keypad .operator {
    background-color: #ffc107;
}

.keypad .operator:hover {
    background-color: #ffb300;
}

.keypad .equals {
    background-color: #0d6efd;
    color: white;
}

.keypad .equals:hover {
    background-color: #0b5ed7;
}

.keypad .utility {
    background-color: #6c757d;
    color: white;
}

.keypad .utility:hover {
    background-color: #5a6268;
}

.history-panel {
    margin-top: 20px;
    max-height: 300px;
    overflow-y: auto;
    border: 1px solid #dee2e6;
    border-radius: 5px;
}

.history-item {
    padding: 10px;
    border-bottom: 1px solid #dee2e6;
    cursor: pointer;
}

.history-item:hover {
    background-color: #f8f9fa;
}

.history-item:last-child {
    border-bottom: none;
}

.dark-mode {
    background-color: #121212;
    color: #ffffff;
}

.dark-mode .calculator {
    background-color: #1e1e1e;
    box-shadow: 0 4px 12px rgba(0, 0, 0, 0.3);
}

.dark-mode .display {
    background-color: #2d2d2d;
    color: white;
    border-bottom: 1px solid #444;
}

.dark-mode .keypad button {
    background-color: #333;
    color: white;
}

.dark-mode .keypad button:hover {
    background-color: #444;
}

.dark-mode .history-panel {
    border: 1px solid #444;
}

.dark-mode .history-item {
    border-bottom: 1px solid #444;
}

.dark-mode .history-item:hover {
    background-color: #2d2d2d;
}

.theme-toggle {
    position: absolute;
    top: 20px;
    right: 20px;
}

@media (max-width: 576px) {
    .calculator {
        max-width: 100%;
        margin: 0;
        border-radius: 0;
    }
    
    .keypad button {
        padding: 15px;
        font-size: 1rem;
    }
}