To do Alt + P T H on Mac in Excel, download and install Accelerator Keys, then press Option, followed by P, T, and H.
Command: Themes
This is how to do Alt + P T H on Mac in Excel with Accelerator Keys, the native ribbon and alt key shortcut solution for Mac users who get more done with Excel.
Alt + P T H opens the Themes gallery to apply a coordinated set of colors, fonts, and effects to your workbook. Themes help maintain consistent formatting across your spreadsheets and make it easy to change the overall look with a single click.