The live chat is only available from 9AM to 6PM Beijing Time, for instance that would be
- Central European Standard Time: 3AM to 12PM
- Eastern Standard Time: 8PM to 5AM
- Pacific Standard Time: 5PM to 2AM
On Sundays they are not available at all!
Outside of their office hours, you can leave a message for the Cssbuy support team and they promise to get back to you.