What is the difference between CSS and SCSS?

In addition to Idriss answer:

CSS

In CSS we write code as depicted bellow, in full length.

body{
 width: 800px;
 color: #ffffff;
}
body content{
 width:750px;
 background:#ffffff;
}

SCSS

In SCSS we can shorten this code using a @mixin so we don’t have to write color and width properties again and again. We can define this through a function, similarly to PHP or other languages.

$color: #ffffff;
$width: 800px;

@mixin body{
 width: $width;
 color: $color;

 content{
  width: $width;
  background:$color;
 }
}

SASS

In SASS however, the whole structure is visually quicker and cleaner than SCSS.

• It is sensitive to white space when you are using copy and paste,

• It seems that it doesn't support inline CSS currently.

  $color: #ffffff
  $width: 800px
  $stack: Helvetica, sans-serif
  
  body
    width: $width
    color: $color
    font: 100% $stack
  
    content
      width: $width
      background:$color
  

CSS is the styling language that any browser understands to style webpages.

SCSS is a special type of file for SASS, a program written in Ruby that assembles CSS style sheets for a browser, and for information, SASS adds lots of additional functionality to CSS like variables, nesting and more which can make writing CSS easier and faster.
SCSS files are processed by the server running a web app to output a traditional CSS that your browser can understand.