Each time a WordPress update is released, I have to manually edit core files to override the CCS that is forced into code output. It gets annoying rather quickly and, as a design point of view, should be in the theme's CSS file versus hardcoded as PHP output code.
For example, wp-includes/media.php forces a defined CSS gallery styling output (i.e.
$output = apply_filters('gallery_style', ") for margins, border colors, etc. Core files should focus on processing and leave the CSS styling to the actual theme file. Certainly define an "empty" gallery class in the code, but leaving the styling aspect as part of theme and not something that require a core file edit with each WordPress update.