- Move styles that apply to the following into a new file resources/src/mediawiki.skinning/messageboxes.less
.messagebox, .errorbox, .warningbox, .successbox
- resources/src/mediawiki.skinning/legacy.less should @import the newly created LESS file
- A new feature is added to ResourceLoaderSkinModule which loads those styles when interface-message-box is inside the features array. Please see elements for an example of how this should work.
- Prioritize making sure the styles are consumed in Minerva and not MobileFrontend (T233160)