How does z-index and position fixed work together in css

Answer 1

You can't do that if .fixed element is acting as a holder for any of its children.

This means that if, for example, you set your h3 with an absolute position to the bottom, it will go to the bottom of its parent element.

z-index works the same way. Its value will be inherited by the parent. Since the z-index default value is 0, your .fixed element has a z-index value of 0, and your h3 has first 0 and then 300.