New theme system for the portal

The theme system separates the public presentation from application logic. Each theme has its own manifest file, stylesheet and set of views, and administrators can pick the active theme from the admin panel.

The default theme follows MyDS design tokens: the blue colour scale, Poppins for headings and Inter for body text, plus consistent radii and shadows. Developers can copy the default theme as a starting point for their agency brand.

The theme development standards are documented on the Policy page.