Here are some of the key features of Sass that make it a popular choice for CSS development:

Variables: Sass allows you to use variables to store values that you can use throughout your stylesheet. This makes it easier to manage colors, font sizes, and other styles that you want to use consistently throughout your website. For example, you could define a variable for your brand's primary color and then use that variable throughout your stylesheet.

Mixins: Mixins are reusable blocks of CSS styles that you can use throughout your stylesheet. They can contain any CSS code and can take arguments to customize their behavior. This makes it easier to write complex styles that you can reuse in multiple places without having to copy and paste the same code over and over again.

Functions: Sass functions allow you to perform operations on values and then return a result. This can be used for things like calculating the width of an element based on its height, or converting one unit of measurement to another.

Nested Rules: Sass allows you to nest CSS selectors inside of each other, making it easier to organize and maintain your stylesheet. This makes it easier to see the relationships between styles, and it can help to reduce the amount of repetitive code you need to write.

Partial Files: Sass allows you to break your stylesheet into smaller, reusable partial files. You can then include these partials in your main stylesheet to create a modular and reusable codebase.

Sass is a powerful tool that can help you write more efficient and maintainable CSS. It can help you write code that is easier to read, easier to reuse, and easier to maintain, making it a great choice for any CSS project.