This is great, but it doesn't take into account that often you'll need to put the tool-tip in different positions depending on it's position relative to other content or the window edge, and that input's used that way are likely semantically incorrect.
I gave a workshop about this a few months ago.. based on this great article from A List Apart. Using basically :target and radio/checkboxes you can make even more stuff like drawers, sliders, tabs, material fab-menus and modals.
You can check out the code on gitHub if you want. but let me warn you that the code was made at the workshop, code along style, and lacks proper comments.
The "checked" trick is brilliant! Never thought of that
Great! Very clever, too. Will come in handy! Thank you.