Fix sidebar visual distinction on contributing-code page

[TechGenie-awake]

Fixes

• Fixes Side nav is no visually separated enough from main content area #943 by @possumbilities

Description

Fixes sidebar visual distinction issue on contributing pages by adding background styling and improved spacing to match the design consistency used in legal tools pages.

Technical details

• Added var(--vocabulary-brand-color-soft-gold) background color to sidebar container
• Applied consistent 1em padding and 4.1rem left margin for proper spacing
• Set height: fit-content to ensure sidebar scales appropriately with content
• Removed excessive padding-left: 4.1em that was causing layout issues
• Fixed link visibility by removing white underline background that was masking text on gold background

Tests

1. Navigate to any Contributing Code page (e.g., /contributing-code/)
2. Verify sidebar now has a light gold background that clearly separates it from main content
3. Check that sidebar content is properly contained within the background area
4. Compare with legal tools pages to confirm visual consistency

Screenshots

Problem:

Solution:

Checklist

• My pull request has a descriptive title (not a vague title like Update index.md).
• My pull request targets the default branch of the repository (main or master).
• My commit messages follow best practices.
• My code follows the established code style of the repository.
• I added or updated tests for the changes I made (if applicable).
• I added or updated documentation (if applicable).
• I tried running the project locally and verified that there are no
  visible errors.

Developer Certificate of Origin

For the purposes of this DCO, "license" is equivalent to "license or public domain dedication," and "open source license" is equivalent to "open content license or public domain dedication."

Developer Certificate of Origin

Developer Certificate of Origin
Version 1.1

Copyright (C) 2004, 2006 The Linux Foundation and its contributors.
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Suite D4700
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Everyone is permitted to copy and distribute verbatim copies of this
license document, but changing it is not allowed.


Developer's Certificate of Origin 1.1

By making a contribution to this project, I certify that:

(a) The contribution was created in whole or in part by me and I
    have the right to submit it under the open source license
    indicated in the file; or

(b) The contribution is based upon previous work that, to the best
    of my knowledge, is covered under an appropriate open source
    license and I have the right under that license to submit that
    work with modifications, whether created in whole or in part
    by me, under the same open source license (unless I am
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    in the file; or

(c) The contribution was provided directly to me by some other
    person who certified (a), (b) or (c) and I have not modified
    it.

(d) I understand and agree that this project and the contribution
    are public and that a record of the contribution (including all
    personal information I submit with it, including my sign-off) is
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[possumbilities]

Hi @TechGenie-awake thanks for this, it's definitely heading in the right direction, but since vocabulary is an upstream dependency, localized changes like this should be made in the more localized files (like assets/static/css/style.css) instead.

That way future updates to vocabulary are unimpeded.

[TechGenie-awake]

Thanks @possumbilities ! Moved sidebar styles to style.css and reverted vocabulary changes to prevent upstream conflicts.

[possumbilities]

@TechGenie-awake thank you for the scoping adjustment. Approving.

[possumbilities]

@TechGenie-awake if you respond to the original issue I can credit you!

• Side nav is no visually separated enough from main content area #943