body {
  background-color: lightgray;
  font-family: Arial, Helvetica sans-serif;
  }
  
  #container {
  width:1100px;
  margin:0px auto;
  border:4px solid gray;
  }
/*Segundo Paso*: Configurar Encabezado */
header {
background-color: red;
height: 100px;
width: 100%;
margin: 0px;
text-align: center;
line-height: 100px;
color: antiquewhite;
border-bottom: 2px solid black;
}
/*Tercer Paso: Crear Menu*/
nav ul li {
float: left;
list-style: none;
margin: 20px;
line-height: 10px;
}
/*Quitar Subrayado*/
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; 
/*Usando la función calc*/
width: calc(20% - 20px);
background-color: coral;
min-height: 500px;
padding: 10px;
}
/*Quinto Paso: Modicar el Footer
footer*/
footer{
background-color: black;
color: white;
text-align: center;
height: 30px;
line-height: 30px;
}