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Format>Style>Normal>Modify. Make the changes here>OK.
This is a workbook-specific change. Not global. Watch out when doing this.
It will affect worksheet fonts as well as Row and Column Headers.
An alternative is Tools>Options>General>Standard Font. Make changes here then
close Excel.
Re-open Excel and any New workbooks Row and Column Header Fonts will default
to the changes. Existing/saved workbooks will not be affected.
Use whichever method suits.
Gord Dibben Excel MVP