FIX-CSS-3.5 is a a framework for quickly developing user interfaces and web applications using a set of combined HTML, CSS, and JavaScript assets. It enables developers to quickly prototype, build and deploy modern web applications. It is designed with developers in mind, offering customizable and re-usable components, built with clean and semantic HTML and JavaScript. With FIX-CSS-3.5, developers can create responsive, dynamic, and adaptive web applications for any browser, device, or platform. The framework is open-source, and has been actively developed since 2017. It also offers many ready-to-use components, as well as a quickly growing library of user-contributed components.