Exercise group intro/conclusion spacing

[ascholerChemeketa]

Addresses spacing issues identified by @jjrsylvestre in exercise group intro/conclusions.

I'm not sure the horizontal indent on conclusion makes sense, feels like it should match the intro, not the exercises, but that is what was there historically.

[rbeezer]

For PDF (since I was just doing it) we only indent the exercise themselves.

To keep the two PDF conversions in-sync, I have just started an area in pretext-common.xsl with "Distances and Colors". Don't know if you want to mine that or not? No colors yet, "Sage blue" might be the first. (I think this has been pushed!)

[ascholerChemeketa]

Removed the conclusion indent to match PDF and force pushed.

Leaving exercise indentation as is for now.

[rbeezer]

All CSS, so I will ask @oscarlevin to handle this one. Also, I don't know enough to follow Claude's reservations. Posting that next.

[rbeezer]

The exercisegroup spacing problem is real and the fix works for it, but two of the three CSS changes reach well beyond exercise groups — worth a look before merge.

1. .introduction/.conclusion in _spacing.scss is document-wide, and it wins the cascade. Both intro/conclusion templates set the class from local-name(), so class="introduction" lands on every division intro too — <section class="introduction">, not just the exercisegroup <div class="introduction">. The edited rule (specificity (0,3,0)) beats the high-level :is(section, article, …) > * rule ((0,1,1)) within the same @layer, so every chapter/section introduction and conclusion drops from 1.5em to 0.5em inter-item spacing. The sample article alone has ~10 multi-paragraph section introductions that this re-spaces. The exercisegroup case genuinely needs the fix (those <div> intros matched nothing in the spacing layer), but scoping it — e.g. .exercisegroup .introduction, .exercisegroup .conclusion — would keep it off the division <section> intros.

2. .exercise-like > *:not(:first-child) { margin-top: 1em } is also global. It is at the top level of _exercises.scss (not under .exercisegroup) and outside @layer, so it overrides the layered 1.5em for every exercise — intra-exercise spacing (statement/hint/answer/solution) tightens to 1em document-wide. Reads as intended, just confirming that is the goal and not meant to be exercisegroup-only.

3. Dropping the conclusion margin-left: 40px — agreed. Flush-left intro and conclusion bracketing the indented exercises is a cleaner hierarchy than the historical indent; your instinct in the description is right.

Minor: _spacing.scss still has no trailing newline; sample-article test cases read clean.

Net: #3 is good; #1 and #2 work for exercisegroups but currently apply to the whole document, and #1 in particular silently re-spaces all division introductions via specificity — worth either scoping or making an explicit, tested decision.

Claude Opus 4.8, acting as a review assistant for Rob Beezer