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

nav{
  background-color:cyan;
  text-align:center;
  }