* {
  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 {
  min-height: 500px;
  float: left;
  width: calc(80% - 20px);
  background-color: green;
  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;
}