body {
    text-align: center;
    font-family: Arial;
}
button {
    margin-right: 40px;
}
#nuevo {
    width: 20%;
}
#borrar {
    width: 10%;
}
#bloque div {
    width: 99%;
    height: 10%;
    color: white;
    background: black;
}
#bloque iframe {
    width: 99%;
    height: 89%;
}
#bloque {  
    padding: 5px;
    border:5px solid pink;
    background-color:black;
    width:300px;
    height:400px;  
}
#iframes {
    display: -webkit-box;
    display: -moz-box;
    display: -ms-flexbox;
    display: -webkit-flex;
    display: flex;

    -webkit-flex-wrap: wrap;
    flex-wrap:wrap;
}
#marco {
    background-color: pink;
    padding: 10px;
    margin: 10px;
    border: 3px solid black;
}