People from Poland will already have this by entering a contest.
For people outside of Poland, you will need to use a proxy server. I used proxyhideout.com. Wait until the page loads, then put the following into the proxy URL bar.
Once the page loads, go back to the proxy URL and put this instead.
Close the proxy, go back to Stardoll normally, Log in, and in front of your closet you will have a gift box. Open and enjoy.