Feature: Allow customizing emphasis and bold text colors via html_theme_options

[mmcky]

Feature Request

Summary

Allow users to customize the colors used for emphasis (em) and bold/strong (strong, b) text through html_theme_options in their Jupyter Book _config.yml.

Current Behavior

The theme uses hardcoded colors defined in SCSS:

• Emphasis (italics): Green (#2d9f42)
• Bold/Strong: Brown (#8b4513)

These colors are compiled into the CSS and cannot be changed without custom CSS overrides.

Proposed Solution

Add new theme options to allow customization:

# _config.yml
sphinx:
  config:
    html_theme_options:
      emphasis_color: "#1a73e8"
      emphasis_color_dark: "#8ab4f8"
      definition_color: "#d93025"
      definition_color_dark: "#f28b82"

Implementation Approach

1. Add CSS custom properties (variables) to the theme CSS
2. Expose these as theme options in theme.conf
3. Inject the custom property values via a Jinja template or inline styles

Example CSS variables approach:

:root {
  --qe-emphasis-color: #2d9f42;
  --qe-definition-color: #8b4513;
}

body.dark-theme {
  --qe-emphasis-color: #66bb6a;
  --qe-definition-color: #cd853f;
}

em {
  color: var(--qe-emphasis-color);
}

strong, b {
  color: var(--qe-definition-color);
}

Workaround

Until this feature is implemented, users can override colors with custom CSS. See: https://gist.github.com/mmcky/f3cd498225627424b3237a4b2fdb959f

Additional Context

This feature would make it easier for different QuantEcon projects to have consistent but distinct visual identities without requiring custom CSS files.