Material-ui: Support a second theme

[oliviertassinari]

Summary 💡

Provide a second theme the community would love. It has to take traction on its own to make it a successful effort.

Examples 🌈

One example of a design system that supports multiple themes:

https://seek-oss.github.io/braid-design-system/components/Button

Motivation 🔦

Material Design doesn't have a monopoly on the design systems used by developers and designers. During our last survey, we had 28 feedback to improve custom themes and provide a new theme.

The issues with Material Design:

• Feels a lot like Google. Moving away from this brand can require more overrides than desirable.
• Community love/hate relationship with Material Design. It's polarising.
• I suspect that making a good looking UI could be made easier, too many shadows.

Proposed solution

We bring onboard a full-time designer/developer (somebody with both skills, but has to be a really great designer, no need to have strong development skills) to spin-off a new repository under a different name in the mui-org organization. Build the theme using a limited set of constraints:

• Use the unstyled components we are working on #6218. This should save a lot of time in the process. This would create a healthy constraint to make sure the unstyled components truly deliver (hopefully will force us to improve it). It would also give the unstyled components credibility.
• Use the tooling infrastructure. Our CI infrastructure is pretty solid at this point. (I can't really think of anything that really sucks about it). We can make it work across repositories as we do it with material-ui-x.

A few elements that we could consider setting as constraints but I'm not fully convinced:

• Use the same documentation infrastructure (50% in favor)
• Use the same styling solution (80% in favor)

Related issues

• #18908: Material Design studies x4 themes
• #21911: iOS theme
• #23519: true dark theme
• #21113: document the themes of the community

Benchmark

https://trello.com/c/02I7LL5D/2491-introduce-a-second-theme

[oliviertassinari]

Another advantage of this direction, Material-UI is often associated with Material Design, but that's not the end goal, we provide material to build UIs 🏗️, they have to look and feel awesome. Material Design is one mean to this end.