body {
    margin: 0;
    display: flex;
    justify-content: center;
    align-items: center;
    height: 100vh;
    background-color: #1a1a1a;
}

#calculator {
    font-family: Arial, Helvetica, sans-serif;
    background-color: #000000;
    border-radius: 15px;
    max-width: 500px;
    overflow: hidden;
}

#display {
    width: 100%;
    height: 100px;
    font-size: 5rem;
    text-align: left;
    border: none;
    background-color: #313131;
    color: white;
}

#keys {
    display: grid;
    grid-template-columns: repeat(4, 1fr);
    gap: 10px;
    padding: 25px;
}

button {
    width: 100px;
    height: 100px;
    border-radius: 50px;
    border: none;
    background-color: #464646;
    color: white;
    font-size: 3rem;
    font-weight: bold;
    cursor: pointer;
}

button:hover {
    background-color: #5a5a5a;
}

button:active {
    background-color: #6e6e6e;
}

.operator-btn {
    background-color: #ff9800;
}

.operator-btn:hover {
    background-color: #ffb74d;
}

.operator-btn:active {
    background-color: #ffc947;
}