Sass

Syntactically Awesome Style Sheets

Natively, CSS is verbose, has factorization limitations and can be hard to maintain.

These issues are solved using preprocessors like SASS.

http://sass-lang.com/

Sass: Syntactically Awesome Style Sheets

Preprocessors allow writing CSS in a language with the following features:

• Variables.

• Nesting.

• Mixins.

• Inheritance.

Preprocessors generate standard CSS.

$wt-transition-duration: 0.5s;
$wt-user-list-background-color: blue;

.wt-user-list {

    background-color: $wt-user-list-background-color;

    >li {
        @include transition(transform @wt-transition-duration);
    }
        
}

Preprocessors can generate vendor prefixed CSS using modules like Bourbon.

​http://bourbon.io/

Bourbon - A Lightweight Sass Tool Set