body {
  margin:0;
  padding:0;
  font-family: serif;
}

main, aside, footer, details {
  width:600px;
  margin:auto;
  margin-top:2em;
}

aside {
  background:#aaa;
  padding:2em;
}

main {
  background: #eee;
  padding:1em 2em 1em 2em;
}

footer {
  background: #333;
  padding:1em 2em 1em 2em;
  color:white;
}