Sidecar divider runs through a transparent Nova Header (no header-neighbour top offset) #683

Problem

The Sidecar's divider rule (.nb-sidecar--has-rule::before, shipped in #658) draws from the very top of the .nb-sidecar grid container. On desktop, the Nova Header always overlays the block that follows it, so when a Sidecar is that neighbour and the header's background is transparent (the default), the divider runs straight through the header — across the logo and the navigation — instead of starting where the Sidecar's actual content begins.

Root cause

The divider has no top offset.
packages/block-library/src/blocks/sidecar/scss/_desktop-layout.scss:246-261:

.nb-sidecar--has-rule::before {
  content: "";
  grid-row: 1;
  grid-column: gs / ge;
  align-self: stretch;
  ...
}

All .nb-sidecar-area children share grid-row: 1 (line 18), so this is a single-row grid — align-self: stretch makes the ::before span the entire .nb-sidecar box, top to bottom.

The header's overlay offset is never applied to that box.
packages/block-library/src/blocks/header/frontend/components/index.js:

• Line 33 (and 73): the block after the header gets nb-header-neighbour and, via findPaddingTopTargets (line 288-330), a --nb-header-neighbour-padding-top inline padding-top — enough to clear the absolutely-positioned header (lines 164-175).
• For a .nb-sidecar neighbour, findPaddingTopTargets (line 290-308) does not return the .nb-sidecar element itself. It walks into the sidecar and returns the content area's first child plus the sidebar area children (line 305: [...contentTargets, ...sidebarTargets]). So the padding-top that clears the header lands on the content/sidebar children, pushing the logo/nav/article text down — while the .nb-sidecar container (which owns the ::before divider) never receives any offset and keeps starting at top: 0.

The result: content is correctly pushed below the header, but the divider stays anchored to the untouched top of the container, so it visibly crosses the header band above the pushed-down content.

Repro

Hive LT starter, single post template, Sidecar with a right rail and Divider: Secondary, Nova Blocks 2.7.1, Anima LT 2.0.51, default (transparent) header background.
https://starter.pixelgrade.com/hive-lt/ — any single post.

At 1440:

• Sidecar box starts at y=12.
• Header-neighbour padding-top applied to the content/sidebar children: 479.7px.
• Divider line visible at x=955, running from y=12 straight through the header's logo/nav band, well above where the (correctly offset) content starts.

Workaround in use: setting the Header's backgroundMode to "solid" (opaque header) hides the overlap, but that's a workaround, not a fix — it doesn't work for a transparent-header design.

Expected

When the Sidecar is a header neighbour, the divider should start at the content, not at the raw top of the grid container — i.e. offset by var(--nb-header-neighbour-padding-top), the same amount already applied to the content/sidebar children. (For reference, classic Hive's rule starts below the nav, not at the very top of the page.)

Evidence

Found while building the Hive LT starter: /Users/georgeolaru/Developer/pixelsite-hive-lt/docs/plans/hive-lt-starter/work/p3/REPORT.md, "Round 5" (2026-09-28).

Related

• Sidecar: optional divider rule between content and rail #658 — shipped the Sidecar divider. Its own proposal explicitly called for "Height: from below the site header to the Sidecar's end," but the shipped ::before (line 246) has no such offset — this issue is that gap.
• Design system: one rule model (primary / secondary) for every line — separators, card rules, header rules, sidecar divider #668 — the broader rule-model consolidation; this fix should stay compatible with it (same ::before, just add a conditional top inset).