Very odd.. it seems to be a browser-specific issue.
On Firefox, and SeaMonkey on Windows 10, it all looks like what is shown in the script page and the GitHub distribution (4 button rows.
On Chrome, Brave, Edge, Opera on Windows 10, it has the 4-button rows, but the 'empty' buttons are jogged up a bit compared to the buttons with numbers.
On an iPad or iPhone, Safari, Chrome, Firefox all show the two button-narrow column instead of the 4 button wide pad.
Looks like I need to do some CSS tweaking to have it look the same on all browsers.