Hi Katy,
Admittedly, the Table widget is more limited in terms of styling and interactivity, compared to other widgets like the default shapes. And so, by and large, the primary recommendation when building more involved tables is to use the default shape widgets to customize a table. I can understand that that may be a bigger time investment than using the default Table, but you could also consider saving your customized table in a Custom Widget Library, which you can re-use. Here’s more information on widget libraries:
Widget Libraries
There have been related forum discussions which involved inserting JavaScript into the OnPageLoad to target a specific table widget. That gets into pretty advanced territory, though, outside the typical scope of support–here’s an example:
Table cell border.
If JavaScript is something you’re ready to harness on your end, do feel free to give that a shot. I’m thinking that changing the “border-left” and “border-right” parameters may be a way forward. HTH!