It’s supposed to be used by 2 people taking turns (click twice for the other sign).
- It uses hidden checkboxes for the states (indeterminate means empty, checked means X, not checked means O) and labels for the visible part
- When it starts, a little script (the only js in the demo) sets the states of all checkboxes to indeterminate.
- It uses the
:indeterminatepseudo-classes and sibling combinators to change the states and show who won.
- Once somebody clicks on a checkbox (or in this case, its label) they change it’s state from indeterminate to either checked or not checked, depending on how many times they click on it.
As a bonus, it’s perfectly accessible through the keyboard (although I assume it’s not screen reader accessible).
A <table> would be much more appropriate for the markup, but I decided to sacrifice semantics in this case to make the demo simpler.
All modern browsers support the indeterminate state in checkboxes (for Opera you will need the latest Opera.Next), however this demo doesn’t work on old Webkit (Chrome and Safari) because of an old bug that made the sibling combinators (+ and ~) static in some cases which has been fixed in the nightlies. It should work in Firefox, Opera.next, Webkit nightlies and IE9, although I haven’t tested in Opera.next and IE9 to verify.