[MOOSE-354] FE: Group block left/right padding in editor

[GeoffDusome]

What does this do/fix?

This change removes the extra padding that was applied to core Group blocks when using the theme’s color styles (White, Light, Dark, Brand).

• style.pcss: Drops the --group-themed-default-padding custom property and the rule that added vertical padding plus root horizontal padding to full-width groups inside main (the previous behavior aligned inner content with the global root padding).
• Block style JSON (10-white, 20-light, 30-dark, 40-brand): Removes the spacing.padding entry that used var(--group-themed-default-padding), so themed groups no longer get that default padding from the style variation.
• CHANGELOG.md: Documents the update under [2026.03].

Editors can still control spacing via the block’s own spacing controls; this only removes the automatic themed padding.

QA

Links to relevant issues

• MOOSE-354

Screenshots/video:

• Nested Group blocks no longer override default left/right editor padding: https://p.tri.be/i/e1MAU4

Pull request checklist

• I've added a changelog entry for these changes.
• I've linked to a relevant Jira issue.
• I've captured a screenshot or screencast of the changes and linked it above.

[GeoffDusome]

@dpellenwood @Vinsanity Do either of you know if, because this was an issue on learn.tri.be if I have to also make this update there, or do we port stuff back there?

[spadilha]

🍏 Just double check if the changes in package-lock.json was intentional.

[GeoffDusome]

🍏 Just double check if the changes in package-lock.json was intentional.

Every time I run lando start, npm install runs and then does that to the package.lock file. I don't know why.

[jamiepaul]

🟢

[dpellenwood]

@Vinsanity & @LayaTaal , Is this related to the discussion we had yesterday about padding on group blocks? If so, can we loop Geoff and Marina in on this convo before this gets merged?

[LayaTaal]

@Vinsanity & @LayaTaal , Is this related to the discussion we had yesterday about padding on group blocks? If so, can we loop Geoff and Marina in on this convo before this gets merged?

This is related @dpellenwood. I think we should go over this all once more with design to align on a permanent solution that works for them.

[GeoffDusome]

@dpellenwood @LayaTaal Did we land anywhere here after talking to design? Should I talk to DE? Last I heard from Marina she wanted all padding removed from these Group blocks by default, including top & bottom.

[GeoffDusome]

Re-requested reviews from everyone here as the scope changed per slack here: https://tribe.slack.com/archives/C04N3SZ7QVD/p1777927175330039

cc @dpellenwood @spadilha @Vinsanity @LayaTaal @jamiepaul