Hi,
> At they do not belong to the EPUB adaptive layout specs…
These properties starting with -- are custom properties defined in the following spec:
http://www.w3.org/TR/css-variables-1/
However, the custom properties are currently *not supported* by Vivliostyle.
I included them in the samples with intention to illustrate how you could write styles conveniently *if they were supported* (in some future version of Vivliostyle), but I admit that it is confusing.
I will remove those from the samples. Thank you for pointing out.
--
Toru Kawakubo (川久保 亮)
Vivliostyle Inc.
http://vivliostyle.com