MISSION - Refactor bokeh's theme and styling systems

[trallard]

📌 Summary

Modernise and simplify bokeh's theming system and its accessibility.

📝 Background

Bokeh's theming system is rather rudimentary and only focuses on plots. Interactive widgets and components are controlled through CSS files, making consistent styling challenging for end-users. We plan to redesign the theming system, thus allowing for a single and consistent approach to styling plots and interactive components. This will also significantly reduce the library maintenance effort.

Such an improvement will also allow for designing and implementing consistent light/dark styling, adopting accessibility best practices, complying with WCAG, and developing high-contrast and colorblind-friendly themes and color palettes.

🚀 Tasks / Deliverables

Note

See issues labelled as: mission: theming 🪄

ℹ️ References

• Bokeh themes documentation
• Bokeh stylesheets documentation
• WCAG 2
• Starting in 3.5 - there has been some improvement made towards leveraging CSS see: Add support for CSS-based theming on the canvas bokeh/bokeh#13828
• Issue related to theming and colourblindness Improve usability with color vision deficiencies bokeh/bokeh#11481