*{
margin: 0px;
padding: 0px;
}

body {
background:#444;
color:#fff;
}

#contenedor {
width: 960px;
margin: auto;
margin-top: 20px;
margin-bottom: 20px;
background: #000;
scroll-behavior: all;
}

header {
height: 150px;
background: #abc;
line-height: 150 px;
}

nav  {
background: orange;
height : 60px;
}

nav h2 {
font-size: 50px;
text-align: center;
line-height: 60px;
}

#contenido {
width: 700 px
height: 800px;
float: left;
background: #123456;
margin-top: 10px;
margin-right: 10px;
margin-bottom: 10px;
}

aside {
width: 250px;
height: 800px;
background: green;
margin-top: 10px;
float: right;
}

footer {
background: blue;
clear: both; 
}