Apply CSS formatting across Drupal nodes

I have a drupal site with a few hundred nodes that I need to all be formatted the same all the way throughout the site, I would think this would be done by applying a CSS stylesheet to format them all the same, Some of the nodes when have been entered have had HTML tags added to them on entry so all this HTML formatting on nodes needs to be over-ridden by the global CSS formatting. ie. all nodes formatted Globally AND NOT Locally.