Which pages affect text area CSS?
CKEditor set its own CSS classes for text areas, but that would not explain why copying the CSS files from a theme to another doesn't change the visualized styles.

The problem here is that simply changing the files used by a theme doesn't change the used styles; you need to let Drupal know the theme has been changed, and this can be done in two ways:


you select a different theme as default one, disable the theme you modified, re-enable it, and select it again as default theme
you force Drupal to refresh the cache it is using, or you empty the cache tables


In the first case, you submit the theme selection form after each operations.