feat: implement CSS-variable based syntax highlighting for dark mode

[LakshmanKishore]

This pull request refactors how syntax highlighting is handled in the Markdown Viewer application. It removes the use of external Highlight.js theme stylesheets and manual highlighting logic in favor of CSS-based theming mapped to GitHub's color variables. This results in a more consistent appearance across light and dark themes and simplifies the codebase by relying on CSS for styling and automatic highlighting during Markdown parsing.

Syntax Highlighting Refactor:

• Removed external Highlight.js theme stylesheets from index.html and export HTML generation, and replaced them with custom CSS rules for syntax highlighting. [1] [2]
• Replaced manual code block highlighting in script.js with automatic highlighting during Markdown parsing, removing related code and comments. [1] [2] [3]
• Added detailed syntax highlighting rules to styles.css, mapping Highlight.js classes to GitHub color variables for both light and dark themes.

Theme Consistency Improvements:

• Ensured syntax highlighting colors adapt to theme changes by using CSS variables and dynamic color assignments in exported HTML.

Minor Changes:

• Added a newline at the end of styles.css for formatting consistency.

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Project	Deployment	Actions	Updated (UTC)
markdown-viwer	Ready	Preview, Comment	Mar 7, 2026 5:19pm