style.css

* {
    border: 0;
    margin: 0;
    padding: 0;
    font-family: "Courier New", sans-serif;
}

body {
    display: flex;
    justify-content: center;
}

.calculator {
    background-color: #c714c7;
    border: 3px solid black;
    border-radius: 15px;
    width: 400px;
    height: 600px;
    display: flex;
    flex-direction: column;
    align-items: center;
    justify-content: space-between;
    margin-top: 50px;
}

.calculator #display {
    border: 1px solid black;
    border-radius: 3px;
    background-color: #ffffff;
    font-size: 48px;
    width: 360px;
    height: 70px;
    margin: 20px;
    display: flex;
    justify-content: space-between;
    align-items: center;
}

.calculator #display p {
    margin-right: 10px;
}

.calculator #display #sign {
    margin: 0 0 0 10px;
}

.calculator .buttons div {
    margin-bottom: 20px;
}

.calculator .buttons button {
    border: 1px solid black;
    border-radius: 40px;
    font-size: 30px;
    width: 80px;
    height: 80px;
}

.buttons button {
    background-color: #f89a8f;
}

#backspace {
    width: 160px;
}

#add,
#subtract,
#multiply,
#divide,
#negate,
#all-clear,
#backspace {
    background-color: #e06b5e;
}