Canvis a "Use a design system"

Is your feature request related to a problem? Please describe.
Decidim doesn't currently rely on a design system for shaping the products design and implementing it's interfaces. This lack of coherent ans single source of truth shared by Product, Design, and Dev worsens technical and UX debt over time. Aditionnaly, the implementation and use of a design system will positively impact product velocity, dev-design collaboration, and external contributions from other members of the community.

Describe the solution you'd like
Decidim should implement an existing design system known to work well with tailwind, which offers good flexibility for theming and a large collection of desktop and mobile components, and open source such as Daisy UI.

Describe alternatives you've considered
One alternative would be to create Decidim's own custom design system, but this is considered highly impractical as a design system is a product in itself.

Another alternative would be to use other existing design systems such as Material design (Google), Carbon (IBM) but these either aren't designed to work well with tailwind, offer less flexibility, and promote imperialist corporate culture which goes against the very principles and values of Decidim. Other open source design systems are considered too risky in our opinion because they lack any business model. The risk here would be to switch Decidim to a unmaintained design system, as was the case with Zurb Foundation (more below on this).

Additional context
Decidim was initially based on a design system called Zurb Foundation (which is highly unadapted for mobile experience btw), and is still fixing remaining UI debt from this era. Since 2016, Octree had extensive experience in building diverse professional digital products with Zurb Foundation and Material Design (responsive data-oriented web-apps, carpooling web apps, mobile apps), and decided to switch over all their products to tailwind + Daisy UI during the past 2 years.

Based on our experience, we are confident Daisy UI offers a good balance between flexibility, diversity, responsiveness, and theme customization without sacrificing the values of open source.

Additionally, Daisy UI has a business model, which makes it a good candidate for prolonged viability, where other open source systems don't: it has an extensive collection of components free and open to use for all, but paywalls only advanced, business-oriented components such as ones used by corporate client interfaces or ready to use templates.

While we have not tested all the design systems out there, we are certain that the most important step lies in starting with an existing one rather than none.

Does this issue could impact on users private data?
Not at all.