body {
    margin: 0;
    display: flex;
    align-items: center;
    justify-content: center;
    height: 100vh;
    background-color: hsl(0, 0%, 95%);
    font-family: Arial, Helvetica, sans-serif;
}

#calculator {
    background-color: hsl(0, 0%, 20%);
    border-radius: 15px;
    max-width: 400px;
    width: 100%;
    box-shadow: 0 10px 20px rgba(0, 0, 0, 0.3);
    overflow: hidden;
    padding: 20px;
}

#display {
    width: 100%;
    padding: 20px;
    font-size: 3rem;
    text-align: right;
    border: none;
    background-color: hsl(0, 0%, 25%);
    color: white;
    box-shadow: inset 0 -3px 5px rgba(0, 0, 0, 0.2);
    border-radius: 10px;
    margin-bottom: 20px;
}

#keys {
    display: grid;
    grid-template-columns: repeat(4, 1fr);
    gap: 15px;
}

button {
    width: 100%;
    height: 80px;
    background-color: hsl(0, 0%, 35%);
    color: white;
    font-weight: bold;
    border-radius: 10px;
    font-size: 1.5rem;
    cursor: pointer;
    border: none;
    transition: background-color 0.3s, transform 0.2s;
    box-shadow: 0 5px 10px rgba(0, 0, 0, 0.2);
}

button:hover {
    background-color: hsl(0, 0%, 45%);
}

button:active {
    background-color: hsl(0, 0%, 55%);
    transform: translateY(2px);
}

.operator-btn {
    background-color: hsl(44, 100%, 50%);
}

.operator-btn:hover {
    background-color: hsl(44, 100%, 60%);
}

.operator-btn:active {
    background-color: hsl(44, 100%, 70%);
    transform: translateY(2px);
}