When you try to modify a table in Wordpress, it doesn't seems working at all. It's because you cannot override the theme configuration by using simple formulas such as cellpadding or cellspacing.
What you need to do is to try to change in very single cell in the table. For example:
After hide featured image in Wordpress (from startGBC.com)
I don't know what happened to the recently Wordpress update, but I really hate the way that my featured image being added to inside the post. So what I do is simply to remove featured image on posts.
Step 1: open your style.css or custom css in your theme