fix(markdown): update monospace font-face for preformatted code blocks on Windows

[bmuenzenmeyer]

Description

At @avivkeller's suggestion nodejs/doc-kit#910 could be fixed upstream in ui-components, so as to improve all usages

Validation

Setup: add this to any markdown on the site

### 909 Debug Test

```text
┌────────────────────────────────────────────────────────────────────────────────────────────────┐
│                                              href                                              │
├──────────┬──┬─────────────────────┬────────────────────────┬───────────────────────────┬───────┤
│ protocol │  │        auth         │          host          │           path            │ hash  │
│          │  │                     ├─────────────────┬──────┼──────────┬────────────────┤       │
│          │  │                     │    hostname     │ port │ pathname │     search     │       │
│          │  │                     │                 │      │          ├─┬──────────────┤       │
│          │  │                     │                 │      │          │ │    query     │       │
"  https:   //    user   :   pass   @ sub.example.com : 8080   /p/a/t/h  ?  query=string   #hash "
│          │  │          │          │    hostname     │ port │          │                │       │
│          │  │          │          ├─────────────────┴──────┤          │                │       │
│ protocol │  │ username │ password │          host          │          │                │       │
├──────────┴──┼──────────┴──────────┼────────────────────────┤          │                │       │
│   origin    │                     │         origin         │ pathname │     search     │ hash  │
├─────────────┴─────────────────────┴────────────────────────┴──────────┴────────────────┴───────┤
│                                              href                                              │
└────────────────────────────────────────────────────────────────────────────────────────────────┘
(All spaces in the "" line should be ignored. They are purely for formatting.)

Before

After

Related Issues

Closes nodejs/doc-kit#909
Closes nodejs/doc-kit#910

Check List

• I have read the Contributing Guidelines and made commit messages that follow the guideline.
• I have run pnpm format to ensure the code follows the style guide.
• I have run pnpm test to check if all tests are passing.
• I have run pnpm build to check if the website builds without errors.
• I've covered new added functionality with unit tests if necessary.

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Project	Deployment	Actions	Updated (UTC)
nodejs-org	Ready	Preview	Jul 17, 2026 9:21pm

[cursor]

PR Summary

Low Risk
Scoped CSS variable override in markdown styles only; no auth, data, or application logic changes.

Overview
Fenced markdown code blocks (pre) now override --font-ibm-plex-mono with a system monospace stack (SF Mono, Menlo, Consolas, etc.) so ASCII diagrams with Unicode box-drawing characters stay column-aligned on Windows.

IBM Plex Mono is still used for inline code and other UI; only content inside markdown pre picks up the stack, matching how nodejs.org already renders diagrams and addressing doc-kit #909.

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[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 74.61%. Comparing base (2335df8) to head (412acb1).
✅ All tests successful. No failed tests found.

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #9015      +/-   ##
==========================================
+ Coverage   74.55%   74.61%   +0.05%     
==========================================
  Files         100      100              
  Lines        8801     8801              
  Branches      325      325              
==========================================
+ Hits         6562     6567       +5     
+ Misses       2235     2230       -5     
  Partials        4        4              

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[Copilot]

Pull request overview

This PR adjusts Markdown fenced code block typography so box-drawing/ASCII-art diagrams render with consistent character widths on Windows by switching those blocks to a system monospace font stack (instead of IBM Plex Mono) via a scoped CSS variable override.

Changes:

• Override --font-ibm-plex-mono within pre to a system monospace stack to avoid per-glyph fallback width mismatches on Windows.
• Add detailed rationale in markdown.css explaining the box-drawing glyph issue and why the override is scoped to pre.

---

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[github-actions]

📦 Build Size Comparison

Summary

Metric	Value
Old Total First Load JS	10.64 MB
New Total First Load JS	10.64 MB
Delta	0 B (0.00%)