Material UI is a CSS framework and set of React components that incorporate Google’s Material Design. Components include buttons, drop downs, menus, switches, toolbars, and more.

.

Motherplate: A bare bones responsive boilerplate

Motherplate is a bare bones HTML5, CSS3, and SCSS responsive boilerplate. It doesn’t include any visual styling or components, just bare bones CSS to get started with.

A bare bones responsive SCSS boilerplate for web designers

Flexy Boxes: A flexbox code generator and playground

Flexy Boxes is a flexbox code generator and playground in one. Just set the options for your flexboxes, preview them, and then output the code.

CSS-Flip: A CSS BiDi flipper

Need to generate left-to-right or right-to-left CSS? CSS-flip does that for you, from your source. It supports a variety of properties, including borders, margins, padding, and more.

Fluidity: Making HTML 100% responsive

Fluidity is a tiny bit of CSS (107 bytes total) that fixes the part of HTML that isn’t completely responsive. It makes changes to the way images, tables, iframes, preformatted text, and canvas elements, so that they’re completely responsive.

Code Guide by @mdo: Standards for sustainable HTML and CSS

This Code Guide by @mdo is a fantastic guide to create sustainable, flexible, and durable HTML and CSS. It includes guidelines for syntax, attribute orders, classes, comments, and more.

Standards for flexible, durable, and sustainable HTML and CSS. — http://mdo.github.io/code-guide/