mini.css is a tiny CSS toolkit (under 7KB gzipped) that works well on most modern browsers and devices and allows you to customize it quickly and easily. It's written in Sass and tries to make use of HTML5 semantics and modern patterns to deal with common web design problems.
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The whole framework is built on flexbox and works really well on most platforms.
Pro Active developer
The developer is actively maintaining the project and responding to any issues and questions.
The framework is really tiny, under 7KB gzipped.
This is what makes mini.css stand out, because it looks like a pretty powerful library and it still is under 10KB.
It works great on all devices, mobile websites are really easy to develop and view.
Few flavours so far, but there is a lot of space for customization.
Pro Great documentation
From basic syntax, templates, examples, customization to-dos and don'ts. The documentation is pretty great.
Pro Supports CSS custom properties (var)
No other framework supports CSS variables right now (as of November 2017). The latest alpha of mini.css supports this feature, making customization even easier.
ARIA rules are a priority and it works very well for all users.
Works really well with screenreaders.
Git repo has been archived so it's pretty unlikely to receive bug fixes or new features.
Con Not widely used
A large community is always an advantage especially for open source projects. It means better documentation, continued development, and lowers the possibility for the project to be abandoned in the future since the probability for someone from the community to keep maintaining it is larger if the community is larger.
Con Single developer
There is no team developing this framework, except one guy.