April 2026 monthly summary for jupyterlab/jupyterlab focusing on CSS styling modernization and maintainability. Key work centered on adopting CSS variables to unify theming across the UI, together with fixes to linting configuration to ensure reliable, scalable styling practices. This work delivers tangible business value by enabling faster theme iterations, reducing risk of regressions in UI styling, and improving developer productivity. Key accomplishments highlight: CSS variables adoption across core CSS to replace hardcoded values, improving consistency and theming flexibility; hardening stylelint configuration by fixing a YAML parsing issue in .stylelintrc.yaml (declaration-property-value-allowed-list) to ensure CI reliability; and collaboration across the team to enforce variable-based styling patterns (see related commits). Overall impact: stronger visual consistency, easier future styling changes, and a foundation for accessible, theme-driven UI work that reduces maintenance burdens and speeds deployment of UI improvements.