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Bootstrap
The most popular HTML, CSS, and JavaScript framework for developing responsive, mobile first projects on the web.
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axentix
The framework mixing fully customizable components and utility-first classes, leaving the design choice to the developer.
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SurveyJS
Open-Source JSON Form Builder to Create Dynamic Forms Right in Your App. With SurveyJS form UI libraries, you can build and style forms in a fully-integrated drag & drop form builder, render them in your JS app, and store form submission data in any backend, inc. PHP, ASP.NET Core, and Node.js.
I'm using Axentix since a while, and all I can say is that it's easy to use. The components can be customized and it gives enough utilities classes to be able to change all the components designs without writing CSS.