Using Sass, you can nest CSS rules within each other. Sass is not only easier to read, but it helps to avoid a lot of duplication of the CSS selectors. This is especially true for highly-nested CSS rules. Let's look at a simple example:

/* Here is some basic Sass that uses nesting */

#outer-frame p {
  color: #ccc;
   width: 90%;
  .danger-box {
    background-color: #ff0000;
    color: #fff;
  }
} 

The preceding Sass code will be compiled and the equivalent CSS code will be generated:

/* This is the CSS that the above Sass is compiled to */

#outer-frame p {
 color: #ccc;
 width: 90%;
}
#outer-frame p .danger-box {
 background-color: #ff0000;
 color: #fff;
}