Spectrum for Adobe XD: Adobe’s Design Language in its Experience Design Tool
MVP.css - Minimalist stylesheet for HTML elements
Responsive HTML images
… adapts your existing HTML images for mobile devices. No mark-up changes needed. Just drop it in and forget about it.
AppControls
… makes it easy to quickly create high-quality custom controls for your iOS apps, Mac apps and for the web.
Apple OS X Lion Buttons in CSS