Thank you for creating this task, @Tacsipacsi – for now, I'm going to move this to the backlog for the reason you named: Timeless is not officially supported by DT per T306730.

I hadn't realized that was not expected. The cause is probably the same as T235459: Timeless treatment of <h2> is somewhat different than Vector and the associated fix is trivial: set border-bottom: none on h2:after rather than h2.

That said, I have a related issue that I stated on the talk page in my feedback about the "Topic" changes. DT is too aggressive about deciding what the stying of the h2 should be IMO. It makes the bad assumption that all skins will be using sans-serif, which Timeless does not. I don't really see why that change was made either and would advocate that DT not style that.

I can file that as a specific ticket, since it's not the same issue, but it is related enough that I thought it was worth bringing up a second time, and the fact that DT does not "support" the skin doesn't mean it shouldn't or that being less opinionated is necessarily supported. No rationale at all is provided on the task referenced, though I can see the related task that the concern is at the "is the feature even available at" level rather than "button not display the exact same" minor decision a skin might take, but even so there isn't rationale. ("I talked to the team" isn't, uh, valid, when what was said wasn't published. :)

In fact, I really dislike that it's not a general constraint that XYZ skins aren't generally supported. Right now the team working on making Special:Prefs work for mobile (T308651) is assuming MobileFrontend is running when that may not be the case for a skin, and that bothers me because it basically promotes code duplication as well as making a false assumption about what I think everyone wants the future to be regarding skins (@Jdlrobson having spent a chunk of time on that over the past 3 years on top of that), which explicit non support of certain skins also does. (Sorry Jon to drag you in, feel free to respond as little as you like.)

In T318238#8251087, @Izno wrote:

It makes the bad assumption that all skins will be using sans-serif, which Timeless does not.

Neither does Vector (since the Typography refresh in 2014), changing to sans-serif was an intentional change that affects Vector just as much as Timeless. Call it good or bad, but it wasn’t an unintentional change based on bad assumption.

In T318238#8251127, @Tacsipacsi wrote:

In T318238#8251087, @Izno wrote:

It makes the bad assumption that all skins will be using sans-serif, which Timeless does not.

Neither does Vector (since the Typography refresh in 2014), changing to sans-serif was an intentional change that affects Vector just as much as Timeless. Call it good or bad, but it wasn’t an unintentional change based on bad assumption.

Where is the task that decided to deviate from/override the typography established in the refresh on talk pages?

In T318238#8251308, @Izno wrote:

Where is the task that decided to deviate from/override the typography established in the refresh on talk pages?

T269950 and related tasks. The font was changed to make talk page sections look less like article sections (see Background > Junior contributors on the task).

In T318238#8251847, @Esanders wrote:

In T318238#8251308, @Izno wrote:

Where is the task that decided to deviate from/override the typography established in the refresh on talk pages?

T269950 and related tasks. The font was changed to make talk page sections look less like article sections (see Background > Junior contributors on the task).

Where is the specific task and design discussion that decided the font was the best way to do that? Why was that rationale sufficient to Be Better than what the Typography Refresh discussion regarding headings had come to?

Moreover, given that this was in the context of adding a lot of other text for these, why does adding the Other Text in the topics not also sufficiently signify that talk page (sections) are "different" from normal section headers?

Change 859133 had a related patch set uploaded (by Bartosz Dziewoński; author: Bartosz Dziewoński):

[mediawiki/skins/Timeless@master] Simplify implementation of heading underlines

https://gerrit.wikimedia.org/r/859133

Change 859133 merged by jenkins-bot:

[mediawiki/skins/Timeless@master] Simplify implementation of heading underlines

https://gerrit.wikimedia.org/r/859133