I will be purchasing a ZED fare on Cathay Pacific for a backup to get out of Hong Kong.

I believe it states dress code is business casual. So, what is the minimum for business casual?
I doubt jeans, tennis shoes and a polo shirt will do.
Get a little spoiled with Delta, and now United, allowing jeans, tennis shoes and t-shirts.
Will dress shoes, slacks and a polo shirt work or do I need a button up shirt.

Thanks for any information.

Tony