title: HTML CSS fixed element only when body reaches a particular point
body: <p>Not sure what the method is or how its achieved. But I'm interested in knowing about it to possibly use it in an upcoming project. What I am referring to is when a block element is at a particular X/Y axis it seems it stops acting as though it were a fixed position element otherwise the element acts as a fixed position element. </p>
  
  <p>I most commonly see this with navigation, where the header and footer are large and the element will stop acting as a fixed element when it reaches the bottom of the header or top of the footer</p>