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