The theme file can be moved from the test to live or vice versa.
You can download the theme form your Test site & upload it to your live site.
Form the Test site, go to the Settings » Hosted Page Themes » Published Theme » Download.
Now go to your live site, Settings » Hosted Page Themes » Upload Theme » Select the downloaded file from your computer.
The uploaded file will list under Installed / Uploaded Themes, click on Configure & Publish Theme to go to the editor and click on publish at the top.
Note: Remember to select the theme named custom on the top left corner
If you have further questions contact our support team firstname.lastname@example.org