The key phrase here is “children of a grid container.” The specification defines the creation of a grid on the parent element, which child items can be positioned into. It doesn’t define any styling of that grid, not even going as far as to implement something like the column-rule property we have in Multi-column Layout. We style the child items, and not the grid itself, which leaves us needing to have an element of some sort to apply that style to.

Now, when the user interacts with the keypad, the value of pin in the parent component is immediately updated.