button {
    width: 100px;
    height: 100px;
    border-radius: 45px;
    border: none;
    background-color: #3b3b3b;
    font-size: 3rem;
    font-weight: bold;
    cursor: pointer;
    color: white;
}

#keys {
    display: grid;
    grid-template-columns: repeat(4, 1fr);
    gap: 10px;
    padding: 25px;
    background-color: #000000;
}

#calculator {
    font-family: Arial, Helvetica, sans-serif;
    background-color: #555555;
    align-self: center;
    border-radius: 15px;
    max-width: 500px;
    max-height: 850px;
    overflow: hidden;
}

#display {
    width: 100%;
    padding: 20px;
    font-size: 5rem;
    text-align: left;
    border: none;
    background-color: hsl(0, 0%, 20%);
    color: white;
}

body {
    margin: 0%;
    display: flex;
    justify-content: center;
    align-items: center;
    height: 100vh;
    max-height: 100vh;
    background-color: hsl(0, 0%, 90%);
}

button :hover {
    background-color: #555555;
}

.orange {
    background-color: orange;
}