calc.css

* {
    margin: 0;
    padding: 0;
}

.fundo {
    background-image: linear-gradient(45deg, black, slateblue);
    height: 100vh;
    color: powderblue;
    font-family: Verdana, Geneva, Tahoma, sans-serif;
    text-align: center;
}

.calculadora {
    position: absolute;
    background-color: rgba(0, 0, 0, 0.6);
    top: 50%;
    left: 50%;
    transform: translate(-50%, -50%);
    border-radius: 20px;
    padding: 15px;
}

.button {
    width: 50px;
    height: 50px;
    font-size: 30px;
    cursor: pointer;
    background-color: rgb(31, 31, 31);
    border: none;
    color: #ccc;
}

.button:hover {
    background-color: slateblue;
}

.div-footer {
    position: absolute;
    bottom: 0;
    left: 46%;
    color: #ccc;
}

#result {
    background-color: white;
    width: 100%;
    height: 32px;
    font-size: 24px;
    color: black;
    text-align: right;
}