body {
  background-color: red;
}

#all {
  background-color: white;
  width: 600px;
  margin-left: auto;
  margin-right: auto;
}

nav {
  background-color: green;
  float: left;
  width: 150px;
}

#content {
  background-color: yellow;
  float: left;
  width: 450px;
}

footer {
  background-color: gray;
  clear: both;
  text-align: center;
}