If your doing it just once for all sheets in the same workbook
Group all the sheets, by selecting the first sheet, Shift and select the last sheet
Then apply the Formatting
It will be applied to all grouped sheets
Don't forget to undo the Grouping
If your doing it just once sheets in different workbooks
Select the whole sheet by clicking in the small square to the Upper Left of cell A1, Copy (Ctrl C)
Goto the second workbook
select the worksheet
Select cell A1
Paste Special Format
If your going to be updating many sheets repeatedly or regularly you would be best to do this via a macro recorded by doing it once with the Macro recorder on and then adjust the code to make it generic ie: to the active worksheet not a specific worksheet