If you want to prevent others from accidentally or deliberately changing the formatting of your Excel spreadsheet, you can lock the formatting. This will prevent anyone from changing the font, font size, colors, or any other aspect of the spreadsheet's appearance.
To lock the formatting, first select the cells that you want to protect. Then, go to the Home tab and click the Format button. In the Format Cells dialog box, select the Protection tab. Finally, check the Locked checkbox and click OK.