I created a number of worksheets in Mac Excel 2008. I have now upgraded to Office 2011 and therefore Excel 2011, and have 'saved as' my worksheets (originally in .xls format) in .xlxs format. But the icon for adding or changing borders to cells cannot be seen. It is clearly visible under 'Fonts' in newly-created .xlsx worksheets.

How can I, then, add borders or change borders in my converted old worksheets?

Thank you in anticipation of help.