body {
    margin: 0;
    display: flex;
    justify-content: center;
    align-items: center;
    height: 100vh;
    background-color: rgb(62, 0, 0);
}
button {
    width: 50px;
    height: 50px;
    border-radius: 50px;
    border: none;
    background-color: rgb(50, 50, 50);
    color: yellow;
    font-size: 3rem;
    cursor: pointer;
    font-weight: bolder;
}
.calc {
    font-family: Arial, sans-serif;
    background-color: rgb(50, 50, 70);
    border-radius: 25px;
    max-width: 500px;
    overflow: hidden;
}
#display {
    width: 100%;
    padding: 20px;
    font-size: 5rem;
    border: none;
    background-color: rgb(70, 100, 70);
    text-align: left;
    color: greenyellow;
}
.keys {
    display: grid;
    grid-template-columns: repeat(4, 1fr);
    gap: 9px;
    padding: 25px;
}
button:hover {
    background-color: rgb(100, 100, 100);
}
button:active {
    background-color: rgb(200, 100, 0)
}
button.operator {
    background-color: rgb(0, 50, 50);
}