This is a pure CSS content panel designed by Mattia Astorino. There are two different transition animation for one we see the second section slide down and for the second one we see the second section just fades into view.
If you are having trouble with the pen, try the archived copy on GitHub
Pure CSS Panels Snippet
See the Pen Pure CSS panels by Mattia Astorino (@equinusocio) on CodePen.0