Restore zIndex on progress bar container to fix onboarding modal centering

[MelvinBot]

Explanation of Change

PR #80460 changed the headerProgressBarContainer style from zIndex: -1 to pointerEvents: 'none'. While pointerEvents: 'none' correctly prevents the progress bar from intercepting interactions, removing zIndex: -1 changed the stacking context for the absolutely positioned progress bar container on web browsers. This affected the flex layout height computation of parent containers, causing the onboarding modal to align to the top of the screen instead of being vertically centered.

This PR restores zIndex: -1 alongside pointerEvents: 'none' so both the accessibility fix and the correct stacking context are preserved.

Fixed Issues

$ #85872
PROPOSAL: #85872 (comment)

Tests

1. Log out and create a new account with a Gmail address
2. Go through the onboarding flow
3. Verify the onboarding modal is vertically centered on the screen (not aligned to top)
4. Verify the progress bar is still visible and animates as you progress through onboarding steps

• Verify that no errors appear in the JS console

Offline tests

N/A — this is a CSS-only change that doesn't involve network requests.

QA Steps

1. Go to staging.new.expensify.com
2. Log in with a new Gmail account
3. Go through the onboarding flow
4. Verify the onboarding modal is vertically centered on the screen
5. Verify the progress bar displays correctly

• Verify that no errors appear in the JS console

PR Author Checklist

• I linked the correct issue in the ### Fixed Issues section above
• I wrote clear testing steps that cover the changes made in this PR
  • I added steps for local testing in the Tests section
  • I added steps for the expected offline behavior in the Offline steps section
  • I added steps for Staging and/or Production testing in the QA steps section
  • I added steps to cover failure scenarios (i.e. verify an input displays the correct error message if the entered data is not correct)
  • I turned off my network connection and tested it while offline to ensure it matches the expected behavior (i.e. verify the default avatar icon is displayed if app is offline)
  • I tested this PR with a High Traffic account against the staging or production API to ensure there are no regressions (e.g. long loading states that impact usability).
• I included screenshots or videos for tests on all platforms
• I ran the tests on all platforms & verified they passed on:
  • Android: Native
  • Android: mWeb Chrome
  • iOS: Native
  • iOS: mWeb Safari
  • MacOS: Chrome / Safari
• I verified there are no console errors (if there's a console error not related to the PR, report it or open an issue for it to be fixed)
• I followed proper code patterns (see Reviewing the code)
  • I verified that any callback methods that were added or modified are named for what the method does and never what callback they handle (i.e. toggleReport and not onIconClick)
  • I verified that comments were added to code that is not self explanatory
  • I verified that any new or modified comments were clear, correct English, and explained "why" the code was doing something instead of only explaining "what" the code was doing.
  • I verified any copy / text shown in the product is localized by adding it to src/languages/* files and using the translation method
    • If any non-english text was added/modified, I used JaimeGPT to get English > Spanish translation. I then posted it in #expensify-open-source and it was approved by an internal Expensify engineer. Link to Slack message:
  • I verified all numbers, amounts, dates and phone numbers shown in the product are using the localization methods
  • I verified any copy / text that was added to the app is grammatically correct in English. It adheres to proper capitalization guidelines (note: only the first word of header/labels should be capitalized), and is either coming verbatim from figma or has been approved by marketing (in order to get marketing approval, ask the Bug Zero team member to add the Waiting for copy label to the issue)
  • I verified proper file naming conventions were followed for any new files or renamed files. All non-platform specific files are named after what they export and are not named "index.js". All platform-specific files are named for the platform the code supports as outlined in the README.
  • I verified the JSDocs style guidelines (in STYLE.md) were followed
• If a new code pattern is added I verified it was agreed to be used by multiple Expensify engineers
• I followed the guidelines as stated in the Review Guidelines
• I tested other components that can be impacted by my changes (i.e. if the PR modifies a shared library or component like Avatar, I verified the components using Avatar are working as expected)
• I verified all code is DRY (the PR doesn't include any logic written more than once, with the exception of tests)
• I verified any variables that can be defined as constants (ie. in CONST.ts or at the top of the file that uses the constant) are defined as such
• I verified that if a function's arguments changed that all usages have also been updated correctly
• If any new file was added I verified that:
  • The file has a description of what it does and/or why is needed at the top of the file if the code is not self explanatory
• If a new CSS style is added I verified that:
  • A similar style doesn't already exist
  • The style can't be created with an existing StyleUtils function (i.e. StyleUtils.getBackgroundAndBorderStyle(theme.componentBG))
• If new assets were added or existing ones were modified, I verified that:
  • The assets are optimized and compressed (for SVG files, run npm run compress-svg)
  • The assets load correctly across all supported platforms.
• If the PR modifies code that runs when editing or sending messages, I tested and verified there is no unexpected behavior for all supported markdown - URLs, single line code, code blocks, quotes, headings, bold, strikethrough, and italic.
• If the PR modifies a generic component, I tested and verified that those changes do not break usages of that component in the rest of the App (i.e. if a shared library or component like Avatar is modified, I verified that Avatar is working as expected in all cases)
• If the PR modifies a component related to any of the existing Storybook stories, I tested and verified all stories for that component are still working as expected.
• If the PR modifies a component or page that can be accessed by a direct deeplink, I verified that the code functions as expected when the deeplink is used - from a logged in and logged out account.
• If the PR modifies the UI (e.g. new buttons, new UI components, changing the padding/spacing/sizing, moving components, etc) or modifies the form input styles:
  • I verified that all the inputs inside a form are aligned with each other.
  • I added Design label and/or tagged @Expensify/design so the design team can review the changes.
• If a new page is added, I verified it's using the ScrollView component to make it scrollable when more elements are added to the page.
• I added unit tests for any new feature or bug fix in this PR to help automatically prevent regressions in this user flow.
• If the main branch was merged into this PR after a review, I tested again and verified the outcome was still expected according to the Test steps.

Screenshots/Videos

Android: Native

N/A — CSS-only change, web platforms only

Android: mWeb Chrome

N/A — CSS-only change, web platforms only

iOS: Native

N/A — CSS-only change, web platforms only

iOS: mWeb Safari

N/A — CSS-only change, web platforms only

MacOS: Chrome / Safari

[MelvinBot]

The failing check build (developmentDebug, false) is unrelated to this PR's changes.

Analysis: The Android build fails at the Gradle settings evaluation phase with:

Could not read script '/home/runner/_work/App/App/node_modules/expo/scripts/autolinking.gradle' as it does not exist.

This is a CI dependency installation issue — the expo package's gradle scripts are missing from node_modules. This PR only adds zIndex: -1 to a style in src/styles/index.ts, which has no impact on Android build configuration or dependencies.

Evidence: Other Android build variants on this same run (build (Debug, true) and build (Expensify Dev, Debug, true)) passed successfully. Other recent PRs (e.g., #85876) do not have this failure. This points to a transient CI environment issue with node_modules installation for this specific job.

Recommendation: Re-run the failing check — this should resolve itself on a fresh CI run.

[MelvinBot]

The failing checks are unrelated to this PR's changes.

Analysis: This PR only modifies src/styles/index.ts (a single CSS property addition). The two failing builds are:

1. build (developmentDebug, false) — Android: Failed with Could not read script '.../node_modules/expo/scripts/autolinking.gradle' as it does not exist. This is a node_modules setup issue in the build environment, not a code issue.

2. build (New Expensify Dev, DebugDevelopment, false) — iOS: The build ran for 23 minutes compiling native dependencies (Airship SDK, RCT-Folly headers) and appears to have hit a build infrastructure issue. No code compilation errors related to this PR's change.

Evidence: The same Build and deploy apps for testing workflow also failed on main at the same time with identical Android/iOS build failures, confirming these are pre-existing infrastructure issues unrelated to this PR. A subsequent run on main succeeded, indicating flakiness.

All code-related checks pass: ESLint, typecheck, all 8 test jobs, prettier, storybook, spellcheck, and perf-tests.