I was thrown off too -- until I realized that Chrome does tabs that way, and it's not confusing there at all. It's just that the post author overlapped them in

I was thrown off too -- until I realized that Chrome does tabs that way, and it's not confusing there at all. It's just that the post author overlapped them in the opposite direction that tabs typically are laid out: the rightmost tab in the CSS version is the highest, instead of the leftmost one like in Chrome / Sublime Text / other noticeably overlapping tabbed applications.