To do Alt + H B D on Mac in Excel, download and install Accelerator Keys, then press Option, followed by H, B, D.
Command: Top and Bottom Border
This is how to do Alt + H B D 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 D top and Bottom Border applies borders to both the top and bottom of selected cells. This creates a horizontal band effect useful for highlighting rows.