If you want to use CSS, and less of it, when building WordPress themes or plugins, you should be using Sass. Sass is the adopted and widely supported CSS compiler for WordPress, which allows you to use variables, mixins, and nesting to write simpler code. In this course Morten Rand-Hendriksen covers practical workflows for incorporating Sass into the development of a WordPress theme, along with Grunt.js, a task runner that translates Sass code into browser-friendly CSS. First Morten walks the viewer through a full production setup, including implementation of version control, Grunt.js, Ruby, and Sass on Windows and Mac. Then he'll present practical workflows for developing a custom theme (based on the _s or Underscores theme) with Sass and shipping "pure CSS" versions to the public.
Note: This course doesn't teach Sass itself. To learn more about the language, watch CSS with LESS and Sass.