A Theme can only be previewed within the Visual Design Editor (VDE). You can not preview an unpublished theme outside of the VDE.
Published theme pages have a "View Store" button in the top menu-bar. This button will open your store in a new browser tab and take you to the page you are currently editing. It will only show you the last published version of the page. You can not preview draft or unpublished work outside of the VDE.
Updated over 4 years ago