To do Alt + H B T on Mac in Excel, download and install Accelerator Keys, then press Option, followed by H, B, T.
Command: Thick Outside Borders
This is how to do Alt + H B T 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 + H B T thick Outside Borders applies thick borders around the outside edge of the selected range. This creates a strong visual boundary around your selection.