.jumbotron {padding:1rem; margin-bottom: 1rem; margin-top:1rem}}
article {display:none;position:absolute; min-width:60em; min-height:6em; background: white; z-index:100;}
span.example {cursor:pointer; margin-left:2em}
span.example:hover {color:orange}
header {height:10em;background-image: url("computer_networking.jpg");background-size:cover;padding:4em}
header h1 {color:white}
section span a {color:darkgray;}
section span a:hover {color:black;}
footer {min-height:2em; background: #023e8a; margin-top:1em}