Bootstrap
Bootstrap is an open source framework for developing with HTML, CSS, and JS. Quickly build your entire app with their responsive grid system and components.
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Foundation by Zurb
Foundation is a responsive front-end framework that make it easy to design beautiful responsive websites, apps and emails that look amazing on any device.
Bulma
Bulma is a free, open source CSS framework based on Flexbox and used by more than 200,000 developers.
Material Design
Material Design is a design framework by Google – backed by open-source code – that helps teams build high-quality digital experiences.
Tailwind CSS
Tailwind CSS is a highly customizable, low-level CSS framework that gives you all of the building blocks you need to build bespoke designs.