#marco {
    border: 10px dashed purple;
    background-color:Lightgreen;
    width: 350px;
    height: 400px;
    position: absolute;
    top: 50px;
    left: 50px;
}

#pantalla {
    border: 1px solid black;
    background-color: Beige;
    width: 245px;
    height: 60px;
    position: absolute;
    top: 50px;
    left: 50px;
}

#botones {
    width: 245px;
    position: absolute;
    top: 150px;
    left: 50px;
}

#botones-numeros {
    background-color:turquoise;
    position: absolute;
    width: 150px;
}

#botones-operaciones {
    background-color:turquoise;
    position: absolute;
    left: 150px;
}

button {
    border: none;
    color: black;
    padding: 10px 15px;
    text-align: center;
    display: inline-block;
    font-size: 16px;
    margin: 4px 2px;
    cursor: pointer;
}

h3 {
    margin: 4px 4px;
    text-align: right;
}

h5 {
   
    text-align: center;
}