Here are some CSS and JavaScript projects you can contribute to, featuring popular and emerging libraries from 2024:

CSS Projects:

1. Tailwind CSS - A utility-first CSS framework for rapid UI development【20†source】【21†source】.
2. Bulma - A modern CSS framework based on Flexbox【18†source】.
3. Bootstrap - The most popular CSS framework for developing responsive and mobile-first websites【15†source】.
4. Foundation - A responsive front-end framework for creating responsive websites and apps【21†source】.
5. Materialize - A modern responsive front-end framework based on Material Design【19†source】.
6. UIkit - A lightweight and modular front-end framework for developing fast and powerful web interfaces【18†source】【21†source】.
7. Chakra UI - A simple, modular, and accessible component library that gives you the building blocks to build your React applications【17†source】.
8. NES.css - A retro, 8-bit style CSS framework【15†source】.
9. Picocss - A minimal CSS framework for semantic HTML【15†source】.
10. Blaze UI - An open-source modular toolkit for building websites【16†source】【19†source】.
11. Vanilla Framework - A simple, extensible CSS framework from Canonical【16†source】【19†source】.
12. Cirrus - A component and utility-centric SCSS framework【16†source】.
13. PatternFly - A UI framework for enterprise web applications【16†source】.
14. Carbon Components - The component library behind IBM's Carbon Design System【16†source】.
15. Open Props - CSS custom properties to help accelerate adaptive and consistent design【19†source】.
16. Tachyons - A functional CSS framework emphasizing readability and simplicity【19†source】.
17. Material Components Web - Modular and customizable Material Design UI components【16†source】.
18. Beer CSS - Build Material Design interfaces quickly【16†source】.
19. HiQ - A simple CSS foundation with responsive typography and input styling【16†source】.
20. Stacks - UI components used by Stack Overflow【16†source】.

JavaScript Projects:

1. React - A JavaScript library for building user interfaces by Facebook.
2. Vue.js - A progressive JavaScript framework for building user interfaces.
3. Angular - A platform for building mobile and desktop web applications.
4. Svelte - A radical new approach to building user interfaces.
5. Next.js - A React framework for server-side rendering and static site generation.
6. Nuxt.js - A framework for creating Vue.js applications with server-side rendering.
7. Gatsby - A React-based framework for creating fast websites and apps.
8. Meteor - A full-stack JavaScript platform for developing modern web and mobile applications.
9. Ember.js - A framework for creating ambitious web applications.
10. Preact - A fast 3kB alternative to React with the same modern API.
11. Alpine.js - A rugged, minimal framework for composing JavaScript behavior in your HTML.
12. Lit - A simple library for building fast, lightweight web components.
13. Redux - A predictable state container for JavaScript apps.
14. D3.js - A JavaScript library for producing dynamic, interactive data visualizations in web browsers.
15. Three.js - A cross-browser JavaScript library and API used to create and display animated 3D graphics in a web browser.
16. Node.js - A JavaScript runtime built on Chrome's V8 JavaScript engine.
17. Express.js - A fast, unopinionated, minimalist web framework for Node.js.
18. Socket.IO - Enables real-time, bidirectional and event-based communication.
19. Electron - Build cross-platform desktop apps with JavaScript, HTML, and CSS.
20. Ionic - A complete open-source SDK for hybrid mobile app development.

These projects are actively maintained and have thriving communities, making them excellent choices for contribution and collaboration.