Like themes for a document
Please edit your question to provide greater detail as it is not clear what you mean by “theme.”
You can create a template (File > Save As Template…) that various documents can be based on. This is most likely the closest idea of a “theme” I can think of that relates to ODF text documents.
EDIT: It appears this question relates to OOXML document themes, support for which is currently lacking in LO. The related bug reports are: