How do you alter the width of your tables?

My forums must be at 100% because they use the width of the screen, I want to make it so it looks narrower, which template do I edit for that?

[Admin]

Edit the style properties.

[qti]

I want to set different widths for forum homepage and forum display (e.g. to a narrower fixed width so they look not so "empty" - I've modded the vb to look cleaner), and set showthread to 100% to accommodate wide images and picture attachments?

thanks a lot