Distinguish series from non-serial groups (chapter numbers)

[3b1b]

Distinguish series from non-serial groups (chapter numbers)

[vincerubinetti]

From Grant in other issue:

Some groups of topics (linear algebra, calculus, differential equations, neural networks) are meant to be a contiguous series, whereas all the others are more just collections of topics with similar topics/genres. It might make sense for the design under the "by topics" tab to reflect this.
Then, for those groups which are meant to be series, it might make sense to display the chapter numbers with a separate design around their titles.