I haven't verified this, but I really doubt that this, or any other CSS-only solution, will work with elements constrained in an `overflow: hidden` block with a fixed height too short to display the tooltip. Which is a fairly common scenario when building app UIs. Most of the work done by Javascript tooltip libraries is figuring out the correct position relative to the <body> tag and appending the tooltip element outside of normal flow constraints.

Also, a good JS solution will dynamically reposition the tooltip if the requested orientation results in the tooltip being clipped by the viewport (eg. switch from right to left, top to bottom).