.container {  
background-color: rgb(180,180,180);  
width: 40em;  
margin-right: auto;  
margin-left: auto;  
}
header {
  background-color: red;
}
nav {
background-color: firebrick;
width: 200px;
}
article{
    background-color: darkseagreen;
    flex: 1;
  
}
footer{
    background-color: darkolivegreen;
}