calcu.css

.calculadora { border: 3px red ridge; width: 250px; text-align: center;
    background-color: bisque; }
.calculadora button{
    height: 50px;
    width: 50px;
}
#resultado{
    display:block;
    text-align: center;
    font-size: 40px;
    margin-bottom: 5px;
    width:242px;
    height: 100px;
    line-height: 100px;
    background-color:whitesmoke;
    border-radius: 25px;
}
.calculadora input.ancho{
    width: 150px;
    text-align: center;
}