<!DOCTYPE html>
<html>

<style>
.fixed-pos{
  position: fixed;
  background: green;
}
</style>

<body>

<p>You should see no red.</p>

<div class="fixed-pos" >
  <div>
    XXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXX
  </div>
  <div>
    YYYY
  </div>
</div>

</body>
</html>