body 
  {background-color: lightgray;font-family: Arial, Helvetica, sans-serif;}
  
  #container { width: 1100px; margin: 0px auto; border: 4px solid gray;
  }
  header 
  {background-color:red;height:100px;width:100%;margin:0px;text-align:center;line-height:100px;color:antiquewhite;border-bottom:2px solid black;}
  nav ul li {float:left;list-style:none; margin:20px; line-height:10px;}
  a {text-decoration: none;}
  ul{text-align: center; display: inline-block;}
  #content{float:left;width:calc(80% - 20px);background-color:green;min-height:500px;padding:10px;}
  .article{color:white; margin-top:15px; margin-bottom:15px; border-bottom:1px solid white; padding-bottom:20px;}
  aside {float:left; width:calc(20% - 20px); background-color:coral; min-height:500px; padding:10px;}
  footer {background-color:black; color:white; text-align:center; height:30px; line-height:30px;}
  .clearfix{clear:both;}