Unable to save custom cell styles

I am trying to save some custom cell styles in Excel/Office 365 (using Windows 7) so that they appear in any new workbook I create. I have followed the instructions here: https://support.office.com/en-us/article/save-cell-styles-to-use-in-all-new-workbooks-0b3905c5-45d0-4ad4-be39-571f445d30cb numerous times to no avail. Any help/advice would be appreciated.