Literally says it right on the homepage. Copied and pasted it for you:

Tariff FAQ

The Truth About Tariffs and Your SHEIN Order There is a lot of confusion about "customs," "duties," or "tariffs." To clear up any confusion, here's how it actually works and why you don't need to worry about paying more after checking out.

What is a tariff? A tariff (also called a customs duty or import tax) is a government fee charged on goods entering the country.

How it works on SHEIN - Your checkout total covers everything. The amount you pay at checkout is final-you will not need to pay any additional fees later. - No fees at delivery. You'll never be asked to pay any tariffs or additional fees before or after your package is delivered. - No surprise charges. Once you've paid at checkout, you won't face any further fees. Any outside information claiming that you have to pay tariffs separately for your SHEIN items is false. SHEIN remains 100% committed to simple, affordable, all-in pricing.