Add To Cart enlarges variations only once

If a user hits add to cart without choosing any variations,
the variations drop down button enlarges. This only happens once though, and if the user misses it, they may keep hitting add to cart without seeing anything happen.

Ideally, I’d like to know if there is a way to allow a default variation so that the product will be added to the cart no matter what.

Or, barring that, is there a way to make the variations enlarge each time or highlight them in some other way- perhaps with a red outline and an error message that tells the user they must choose a variation?

Thanks

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