<div id="fix"> This is a very long sentence, very very very long. And I have more to say about this very long sentence. Hope you don't get bored.</div>
<div id="content">We can't see the content.</div>

div{
  font-size:20px;
  font-family:sans-serif;
  padding: 10px;
  color:white;
}
#fix{
  background:red;
  position:fixed;
  top:0;
}
#content{
  background:green;
  height: 100px;
}