Changing Headerline Font

I am trying to change the headerline to have white font where the text inside my tables I would like white. Does anyone know how to do this?

Also, there is a bunch of space, I saw a thread where a fix was to make the <td></td> together instead of stacked to fix. My question is, where do you see the <td> tags, what file do I modify and where?

Sorry new to this plugin and wordpress

https://www.ads-software.com/extend/plugins/custom-tables/