although the css has been written so that it works with many themes out of the box (see http://www.wp-pizza.com demos – all themes use the same default stylesheet) it is also deliberately kept quite bland.
So the chances are, you will probably want to adjust some things (i.e css) here and there to work and fit in with your particular theme.

Note: If the theme you are using already provides an option somewhere to enter your custom css, you could enter your custom css declarations there instead of using the file editing options below

if you want to or have to edit files because you have no other means of modifying your css declarations, copy the wppizza/css/wppizza-default.source.css (or wppizza/css/wppizza-responsive.source.css if using the responsive style) as wppizza-default.css (or wppizza-responsive.css) to your (child)theme directory (so it does not get overwritten by future updates of the plugin) and edit as required.

alternatively (and possibly better as any future updates to the main css will still be reflected), just copy wppizza-custom.css to your (child)theme directory and only overwrite the styles you need to override.

if you want to customise the *admin* css create “wppizza-admin-custom.css” in your theme directory to overwrite particular classes used in the admin css

(this file will be read AFTER the main default.css). “Include css” has to be enabled for this to apply

PS: Optionally as of version 2.8.9.7 – you could use a subdirectory in your (child)theme called wppizza for all your customised wppizza templates.

Generally speaking, you would be well advised to use a child theme (if your theme does not already provide one, just create one – http://codex.wordpress.org/Child_Themes – if you want to mess around with css etc