I have read about SCSS and LESS. But I can't understand the differences clearly. I know SCSS and LESS both have more functionality of CSS (I mean extension of CSS).
What is different between SCSS and LESS? Which one is better?
Both Sass and Less are CSS preprocessors.
From keycdn.com
A CSS preprocessor is basically a scripting language that extends CSS and then compiles it into regular CSS.
So Sass and Less don't change the functionality of CSS, as they are compiled into plain old CSS. What they do is make it easier to write and maintain CSS with tools such as mixins, nesting, variables, and more.
SCSS, which stands for 'Sassy CSS' is one of two syntaxes for Sass.
From the sass reference:
The second and older syntax, known as the indented syntax (or sometimes just "Sass"), provides a more concise way of writing CSS.
Both Sass and Less have very similar features. There are syntactical differences, for example, Sass uses $ for variables whereas less uses @ .
There are some slightly more subjective differences, this website claims that "LESS Has More User-Friendly Documentation Than SCSS", however personally I have found the SCSS documentation and examples very easy to use.