They don't hide the fact they are based in China. From their 'about us' page:
We are the Chinese on-line shop which sells the products under the brand Okdress and mainly aiming at women fashion product...
UK won't apply so you're only hope is to rely on their policy:
Size Errors
2. We provide a modification service for our customers, who can send back the dress to us and get the dress modified within 7 working days. In this case, we are responsible for the shipping costs including returning and sending back after modification.
3. Customers can also return a dress with measurement errors, and will receive a refund for the purchase price plus shipping.
If all that fails you may be able to your money back from the payment provider such as your credit card.