Investigation (issue #2969 / sticky tabs on PRs)

Validation of current code

Pull request detail already uses the same sticky-row markup as issue detail:

<div class="sticky-tabs-sentinel …"></div>
<div class="sticky-tabs-row d-flex align-items-center mb-5">
  <ul … class="tabs nav nav-tabs nav-tabs-line …"></ul>
  <a … class="more-info side-info more-info-dock …"></a>
</div>

And base.css already sets sticky on that row:

.sticky-tabs-row {
  position: sticky;
  top: 0;
  z-index: 990;
  …
}

So adding Bootstrap .position-sticky is not filling a missing sticky declaration on PR pages. .sticky-tabs-row already has position: sticky. Bootstrap .position-sticky is position: sticky !important, which mainly changes cascade priority.

Likely root cause of “works on issues, not on PRs”

There is an intentional exception from issue #2954 / issue #2969:

html:has(.revision-diff) .sticky-tabs-row {
  position: static;
}

• Issue detail pages rarely contain .revision-diff, so .sticky-tabs-row stays sticky.
• PR File Changes embeds RevisionDiffPanel (.revision-diff). That rule forces the tab row back to position: static.
• .revision-diff > .head is itself sticky at top: 0 (diff toolbar / path filter). Sticky nav tabs were disabled so they would not compete with that sticky diff head.

That also explains why adding .position-sticky can “fix” File Changes: !important overrides the position: static exception and re-enables sticky tabs even when a revision diff is present.

On PR tabs without .revision-diff (Activities, Commits, Builds, Code Comments), sticky should already match issue detail. If those tabs also fail to stick, that would be a different bug than the revision-diff exception.

Alternatives (if File Changes sticky is desired)

Recommendation (pending Q1–Q2): Prefer B if the observed failure is File Changes only (current design). Prefer C if sticky primary tabs on File Changes are a product requirement. Avoid A as the long-term fix because it only wins via !important and does not solve sticky stacking with the diff toolbar.

Clarifying questions

1. On which pull request tabs is the sticky tab row failing?

2. If File Changes is in scope, should primary tabs stick while the revision-diff toolbar is also sticky?

3. Should the follow-up implementation issue also cover Build detail parity / regression checks?

Provisional implementation plan (after answers)

1. Confirm failing tabs (Q1) on a live PR.
2. If Q1=A and Q2=A: no code change; document exception; close with Related link only if needed.
3. If Q2=B: open an Improvement to re-enable sticky tabs on Changes and offset .revision-diff > .head by sticky-row height; update html:has(.revision-diff) rules; verify more-info dock + wrap.
4. If Q1=B/C: investigate scroll/overflow ancestors on PR detail (separate from .position-sticky); do not treat Bootstrap .position-sticky as the fix.
5. After direction is locked: create the implementation issue, link it as Related, and close this Question.

@zaakiy please answer 1 / 2 / 3 with letter choices so we can open the implementation issue with the correct scope.

1. a
2. I need some more specific clarification on what you mean. Try to give examples of exactly what text content I should look for.
3. a

@servicedesk

@zaakiy Thanks — noted 1=A (File Changes only) and 3=A (PR detail only).

Clarifying question 2 with concrete UI text

On a pull request File Changes page, after you scroll down far enough that the PR title / merge buttons are off-screen, there are two separate toolbars involved:

Bar 1 — primary PR tabs (the row with these tab labels):

• Activities
• File Changes
• Commits / Builds (whichever appear for that PR)
• Code Comments
• plus the ⋯ (More info) control on the right

Bar 2 — revision-diff toolbar (directly above the file diffs; look for this controls text):

• placeholder / field: Filter by path
• tooltips / controls: Diff options (gear), Download patch, Toggle navigation
• optionally: Batched suggestions, and a review progress percentage label

Today’s intentional CSS exception keeps Bar 2 sticky at the top of the viewport while you scroll the diffs, and lets Bar 1 scroll away so the two bars do not compete for top: 0.

2. When scrolling File Changes, what should stick?

Please reply with 2=A, 2=B, or 2=C. After that we can close this Question and open the implementation issue with the correct scope (or close with no code change if 2=A).