body {
    display: flex;
    justify-content: center;
    align-items: center;
    height: 100vh;
    background-color: #f7f7f7;
    font-family: 'Arial', sans-serif;
}

.calculator {
    border-radius: 5px;
    box-shadow: 0px 0px 20px 0px rgba(0, 0, 0, 0.2);
    background-color: #3a3a3a;
    padding: 10px;
}

.calculator-screen {
    width: 95%;
    height: 60px;
    border: none;
    background-color: #fff;
    color: #000;
    text-align: right;
    padding: 0 10px;
    font-size: 2em;
    margin-bottom: 10px;
}

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

button {
    height: 60px;
    border: none;
    background: #a5a5a5;
    font-size: 1.5em;
    color: white;
    border-radius: 5px;
}

button.operator {
    background-color: #ff9500;
}

button.equal-sign {
    background-color: #ff9500;
}

button.all-clear, button.backspace {
    background-color: #ff3b30;
}