Syntactically Awesome Stylesheets (Sass) and Leaner CSS (LESS) are both CSS 
preprocessors. They are special stylesheet extensions that make designing easier
and more efficient. Both Sass and LESS compile into CSS stylesheets so that 
browsers can read them. This is a necessary step because modern browsers cannot
read .

Go to this site for differenced between SASS and LESS
    https://css-tricks.com/sass-vs-less/