many times you need to type those values. Instead of typing 

these values a lot of times, why not use sass and write like this:

/* Define variables and values for site */

$bgcolor: lightblue;

$txtcolor: blue;

$fontsize: 16px;

/* Use those variables */

body {

  background-color: $bgcolor;

  color: $txtcolor;

  font-size: $fontsize;

}

Browser does not get Sass code. So, you need a Sass 

pre-processor to convert Sass code into normal css 

by a process called transpiling.