1. Introduction

This tutorial will guide you through the process of integrating SASS (Syntactically Awesome Stylesheets) into your Next.js application. SASS is a preprocessor scripting language that is interpreted or compiled into Cascading Style Sheets (CSS). It allows you to use variables, nested rules, mixins, and more, in your stylesheets, making your CSS more maintainable, themable, and extendable.

By the end of this tutorial, you will learn:
- How to set up SASS in a Next.js project
- How to use SASS features like variables, nested rules, and mixins

Prerequisites:
- Basic understanding of Next.js and CSS
- Node.js and npm installed on your local development machine

2. Step-by-step Guide

Setting up SASS in Next.js

1. Start by creating a new Next.js application if you don't already have one. You can create a new app using create-next-app:
   bash npx create-next-app@latest my-app cd my-app

2. Install sass package:
   bash npm install sass

3. Rename .css files to .scss and update the import in your JavaScript or TypeScript file accordingly.

Using SASS Features

Now that SASS is set up in your Next.js project, you can start using its features.

• Variables: Variables in SASS start with a $ symbol and allow you to store and reuse values throughout your stylesheet.
  ```scss
  $primary-color: #333;

body {
background-color: $primary-color;
}
```

• Nested Rules: SASS allows you to nest your CSS selectors in a way that follows the same visual hierarchy of your HTML.
  ```scss
  .navbar {
  background: $primary-color;

  .nav-item {
  color: white;
  }
  }
  ```

• Mixins: Mixins are like functions for your CSS. They allow you to define styles that can be re-used throughout the stylesheet.
  ```scss
  @mixin transition($property) {
  transition: $property 0.3s ease-in-out;
  }

.btn {
@include transition(color, background-color);
}
```

3. Code Examples

Here's a complete example of a SASS file in a Next.js application:

// Define variables
$primary-color: #333;
$secondary-color: #999;

// Define mixin
@mixin transition($properties...) {
  transition: $properties 0.3s ease-in-out;
}

body {
  background-color: $primary-color;
  color: $secondary-color;
}

.navbar {
  background: $primary-color;

  .nav-item {
    color: white;
    @include transition(color, background-color);
  }
}

.btn {
  background: $secondary-color;
  @include transition(color, background-color);
}

4. Summary

In this tutorial, you've learned how to set up SASS in a Next.js application and how to use key SASS features like variables, nested rules, and mixins. To continue your learning, you can dive deeper into the SASS documentation.

5. Practice Exercises

1. Create a Next.js application and set up SASS.
2. Define a set of color variables and apply them to different elements in your application.
3. Create a mixin for a hover effect and apply it to a button in your application.

Solution and explanations:
- The solution will depend on your application's structure and styles. The key is to practice using SASS features in real-world scenarios. When you get stuck, refer back to this tutorial or the SASS documentation.
- Further practice could involve experimenting with other SASS features like operators, conditionals, and loops.