Add button:focus CSS styles to template Counter button

[bamadesigner]

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Anytime a has specific CSS styles for hover state, it should also have those CSS styles for focus state. This helps to highlight interactivity for keyboard users as well as those who use a mouse.

[dummdidumm]

Thanks for your accessibility PRs! Could add a changeset? Instructions on how to do it are in the main readme; it should be a patch release for create-svelte

[bamadesigner]

@dummdidumm Done! Let me know if I did so incorrectly.