It could be a part of improving the whole theme handling altogether. I think theming would be way easier if the CSS would be split into 2 parts.
- Base CSS: All CSS Code that is unlikely to change (e.g. left frame <=> right frame CSS)
- Theme CSS: All CSS Code that is likely to change (Colors, Fonts, Images, etc.). This is being loaded after the Base CSS, so that it can still overwrite it.
Currently you need to edit a ton of CSS Code in order create a theme for PMA. If the theme css however is reduced to a fraction of the code it become way easier to edit it, I think.
Besides that, a cleanup of the css code would probably also help a lot in reducing the size.