Working with Base Properties
Customizing base_properties.props is the easiest way to modify the style attributes of Plone
UI elements. But it has its caveat:
due to the way the skins tool works, you must have all default Plone base
properties in the file, even if you plan to customize only a small set of
them. If you remove some of the properties from the file, Plone won't be able
to access them anymore.
All this doesn't make the base_properties.props approach ideal for
maintenance, upgrades and customization. That's one of the reasons why it will
be gradually phased out in Plone (also for avoiding the use of DTML in CSS files).
I am not yet aware of how and when this will be implemented, so check for
further updates of this paragraph.
You can find more information about the Plone pre-defined properties in
the file CMFPlone/skins/plone_styles/ploneCustom.css.
You may need to use your own properties in addition to the ones that are
pre-defined in Plone.
Instead of adding new properties to base_properties.props,
it is probably better practice to create a new .props
file in your skin layer and to register a stylesheet that uses it
(instead of the base_properties one - see in the original
DIYPloneStyle/skins/diystyle/renameThisFile.css.dtml
DTML code).