With suggested fixes by @Will Koper, the table now renders correctly.  Yay!

Will's explanation, posted in response to my message to the NICAR-L
list: "Looks like your template is getting appended to the content div
rather than the table, so your selector .mytable td doesn't apply to
any elements because they're all outside the <table> tag.

Also, you should try to minimize DOM manipulation by either caching the
jquery selection in a variable outside of your $.each function or
concatenating your templates and then appending them to the element in
one go."  Will's suggested tweaks:
https://github.com/willkoper/spj-tabletop/blob/master/handlebars3.html