If you click inside the table while editing the page and then go to the Table menu item above the editing box, you then go to "Table Properties" in the dropdown menu and you can set cell spacing and cellpadding. I guess this is in pixels, so fill in "5px" or whatever. Maybe. Somebody correct me if I'm wrong on that.
You can also set border width and width of the table in percentage of the page. This is a littler easier than trying to edit that code. When I do that and save, then check the code again, it is giving me a style statement such as:
<table style="border-collapse: collapse; width: 99.9904%; height: 216.525px;" border="0 px" cellspacing="5px" cellpadding="5px">
I'm still experimenting with this. I have limited experience with CSS, being an old-fashioned html 1.0 sort of person.