body {
    display: flex;
    justify-content: center;
    align-items: center;
    height: 100vh;
    margin: 0;
    font-family: Arial, sans-serif;
    background-color: #f0f0f0;
}

.calculator {
    background-color: #333;
    border-radius: 15px;
    padding: 20px;
    box-shadow: 0 0 10px rgba(0,0,0,0.1);
}

#display {
    width: 100%;
    margin-bottom: 10px;
    padding: 10px;
    font-size: 24px;
    text-align: right;
    box-sizing: border-box;
    border-radius: 10px;
}

.buttons {
    display: grid;
    grid-template-columns: repeat(4, 1fr);
    gap: 10px;
}

button {
    padding: 15px;
    font-size: 18px;
    color: white;
    border: none;
    border-radius: 10px;
    cursor: pointer;
    transition: opacity 0.3s;
}

.btn-clear {
    background-color: #f44336;
    grid-column: 3 / span 2;
}

.btn-number {
    background-color: #607d8b;
}

.btn-operation {
    background-color: #4CAF50;
}

.btn-equal {
    background-color: #607d8b;
}

button:hover {
    opacity: 0.9;
}