To do Alt + H B U on Mac in Excel, download and install Accelerator Keys, then press Option, followed by H, B, U.
Command: Top and Double Bottom Border
This is how to do Alt + H B U 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 U top and Double Bottom Border applies a thin top border and double bottom border. This style is standard in accounting for indicating final totals.