This extension is based on the need to be able to have vertical text orientatin in excel online. See https://excel.uservoice.com/forums/274580-excel-online/suggestions/12431940-there-is-no-text-orientation-option-in-excel-onlin
Click on the extension icon and click on "Start vertial mode". Then click on the cell you want to be vertically aligned. Then click the extension icon again and stop the mode.
It is not yet possible to specify more orientation options
The change will vanish on page reload or after leaving the document