Fix #11881 Side navigation scrolling

[poju3185]

Summary

Fixes #11881
When the side nav was scrolled to its top or bottom limit, further scrolling attempts would unexpectedly propagate to the main content area, causing it to scroll instead. To resolve this issue, I've added the CSS property overscroll-behavior-y: contain; to the .side-nav-scrollable-area class, containing the scroll within the side nav and preventing it from affecting the main content area.

References

https://developer.mozilla.org/en-US/docs/Web/CSS/overscroll-behavior

Reviewer guidance

1. Run the Kolibri Mac app on the browser
2. Open the main side navigation
3. Scroll, and observe the main page content does not also scrolling

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Testing checklist

• Contributor has fully tested the PR manually
• If there are any front-end changes, before/after screenshots are included
• Critical user journeys are covered by Gherkin stories
• Critical and brittle code paths are covered by unit tests

PR process

• PR has the correct target branch and milestone
• PR has 'needs review' or 'work-in-progress' label
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• If this is an important user-facing change, PR or related issue has a 'changelog' label
• If this includes an internal dependency change, a link to the diff is provided

Reviewer checklist

• Automated test coverage is satisfactory
• PR is fully functional
• PR has been tested for accessibility regressions
• External dependency files were updated if necessary (yarn and pip)
• Documentation is updated
• Contributor is in AUTHORS.md

before.mov

after.mov

[github-actions]

Build Artifacts

Asset type	Download link
PEX file	kolibri-0.16.0a0.dev0_git.746.g6c10ecd5.pex
Windows Installer (EXE)	kolibri-0.16.0a0.dev0+git.746.g6c10ecd5-unsigned.exe
Debian Package	kolibri_0.16.0a0.dev0+git.746.g6c10ecd5-0ubuntu1_all.deb
Mac Installer (DMG)	kolibri-0.16.0a0.dev0+git.746.g6c10ecd5-0.4.0.dmg
Android Package (APK)	kolibri-0.16.0a0.dev0+git.746.g6c10ecd5-0.1.0-debug.apk
TAR file	kolibri-0.16.0a0.dev0+git.746.g6c10ecd5.tar.gz
WHL file	kolibri-0.16.0a0.dev0+git.746.g6c10ecd5-py2.py3-none-any.whl

[LianaHarris360]

Thank you for your work on this; the change looks good! Could you please retarget this pull request to the release-v0.16.x branch instead of develop so that this change can be included in the next planned patch?

[poju3185]

@LianaHarris360, sorry I have to create another PR(#11992). This one was automatically closed when I was trying to retarget the release branch.