Using a thumb drive, I imported a large spreadsheet from PC Windows 10 Excel 2010 version 14.0 to Excel for Mac Mojave 2019 version 16.20. The column letters and row numbers and sheet tabs all use a black background. The sheet tabs (excluding the current sheet) all use a dark gray font. The MacOS light/dark appearance does not solve this issue. How can I change the background color to be more legible?