Upscale casual clothes are a mix of semi-formal and everyday clothes. People often wear this style to nice dinners and other events.
Men can wear button-up shirts with smart jeans or polo shirts with dark slacks for upscale casual wear.
For women, upscale casual means they can wear dark jeans with a shimmery blouse, high heels, and gold jewellery, for example. You could also wear a semiformal dress with a denim jacket.
When dressing upscale casually, the rule is to pair a casual piece of clothing with something more elegant and then add elegant jewellery, shoes, and other accessories.