body{
    background-color:#001133;
    background-image:url("backgrounds/stars2.gif");
    background-repeat:repeat;
    color:white;
 font-family: 'Courier New', Courier, monospace;
    margin:0;
    padding:20px;
}

#contenedor{
    width:900px;
    margin:auto;
    background:#111144;
    border:5px ridge silver;
}

#cabecera{
    background:#000080;
    padding:20px;
    text-align:center;
    border-bottom:3px solid white;
}

#principal{
    display:flex;
}

#menu{
    width:220px;
    background:#1d2d6b;
    padding:20px;
}

#menu a{
    color:yellow;
    text-decoration:none;
}

#menu a:hover{
    color:white;
}

#contenido{
    flex:1;
    padding:20px;
}

h1,h2,h3{
    margin-top:0;
}