Introduction to Sass

Learning Goals

• Understand that Sass has two syntaxes: SASS and SCSS
• Understand and apply the basics of Sass to follow the principles of DRY
• Speak to the pros and cons of using a CSS Preprocessor

Vocab

• CSS Preprocessor a program that lets you generate CSS from the preprocessor’s own unique syntax. It extends the default capabilities of CSS. Examples include: Sass, LESS, Stylus and more.
• Compiler converts our preprocessed code into css code so that the browser can understand it. Examples include: Webpack, Node-Sass, Gulp-Sass and many more!

Intro to Sass

Sass stands for Syntactically Awesome StyleSheets. Sass allows you to add more advanced syntax - like variables and functions - to your stylesheets.

Some background on Sass

Sass was originally part of another preprocessor called Haml. It used no curly braces or semi-colons, and the syntax adhered to strict spacing and indentation rules. Like so:

With this version, variables were assigned using ! and CSS styles were defined with =. Pretty different from the CSS you’re used to using now.

Developers liked the additional control we had over writing our stylesheets, but wanted a syntax more similar to vanilla CSS. This is where SCSS comes in.

SCSS

SCSS stands for Sassy CSS (…seriously). In May, 2010 SCSS was introduced with more recognizable syntax.

Although you may see the Sass syntax in the wild, movement has shifted significantly toward SCSS for several reasons:

1. All modern CSS is valid SCSS. That means that you can rename an entire .css file .scss and nothing will yell at you. This is not the case for pure Sass with the .sass file extension.
2. There are no strict rules about indentation. There are still best practices, and if your indentation is all over the place you’ll make your teachers cry, BUT through our tears, your stylesheet will still function properly.

Sass in Action

Our browsers do not understand Sass, or any of the css preprocessors! In order to be able to use Sass in our code, we need something to turn our Sass code into CSS code so that the browser can understand it. One tool that compiles our Sass (among other things) for us is Webpack!

Why would we use Sass?

CSS in large apps can get unruly. Making changes to these large apps is tedious and extremely error prone. Sass makes it easier to change colors, fonts, and other properties by keeping your code DRY. This is the one of the key principles of Sass (and in most programming) - DO NOT REPEAT YOURSELF .

Some of the cool tricks include:

• defining variables that can be peppered across multiple CSS files
• nesting elements to visibly reflect the HTML element relationships
• using math equations to adjust sizes and values
• adjusting colors using more intuitive language like “darken” and “lighten”
• bundling groups of styles together to easily reference throughout your CSS

Variables

One of the most obvious and immediately useful features of Sass is the ability to define variables to store values such as colors. Changes made in one place will be reflected anywhere the variable is referenced.

Similar to JavaScript, variables can hold a variety of data types: numbers, colors, strings, booleans, lists (array like objects), and maps (data structures that are key/value pairs).

Variable Syntax

Variables are defined by a $ immediately preceding the name of the variable (like jQuery), and a colon separating the name of the variable from the value.

$primary-color: lime;

They can then be used anywhere in your stylesheet in place of that style. If I wanted all of my paragraph tags to have this color and my buttons to have it as a background color, my selector would look like this:

p {
  color: $primary-color;
}

button {
  background-color: $primary-color;
}

It’s also nice to avoid typing long, specific styles more than once. Instead we can reference a semantically logical variable.

$frilly-font: "Fantasy", cursive;
$main-font: "Open Sans", sans-serif;

$button-slide-transition: width 2s, height 2s, background-color 2s, transform 2s;

.main-content {
  font-family: $main-font;

  button {
    transition: $button-slide-transition;
  }
}

Nesting

Nesting makes representing relationships between elements in HTML possible in CSS.

For example, if you were writing pure CSS and wanted to target an anchor tag that was within a navigation element that was within a particular header tag, you can wrap the elements inside of each other to show the same visual hierarchy that you are used to seeing in your HTML:

Sass Nesting Example

$grey-dark: #2f3640;
$grey-light: #dcdde1;
$red-dark: #FF0000;

header {
  color: $grey-dark;

  nav {
    background-color: $red-dark;

    a {
      color: $grey-light;
    }
  }
}

header {
  color: #2f3640;
}

header nav {
  background-color: #ff0000;
}

header nav a {
  color: #dcdde1;
}

Nesting & Pseudo-Selectors

A common scenario, when nesting is a good option, is when dealing with pseudo selectors. This makes it very transparent which element’s behavior is being targeted on a particular action.

To target a parent element and apply a pseudo selector, use &:pseudo-selector, as in the following syntax:

a {
  color: black;

  &:hover {
    color: pink;
  }
}

Partials and Importing

One of the main benefits of Sass is having the ability to split your codebase across several CSS files without impacting PERFORMANCE - which brings us to the use of @import with Sass.

@import in CSS

You can have multiple files and import them in CSS, but the use of this at-rule is typically a code smell/bad practice. It blocks parallel downloads of CSS files (each time you use @import it creates another HTTP request).

@import in Sass

In the world of Sass, the @import directive works differently - which is important to know. Although @import is still used to require/import other stylesheets into other files, Sass will simply combine imported sheets into one final CSS file that is served to the browser, making it so multiple HTTP requests aren’t made.

• Note: Adding an @import for the same file more than once will still cause performance issues.

Generally, your structure will have the following:

• Partial files that have an underscore prefix
• A main file where you will be importing these partial files

// _variables.scss

// Colors
$favorite-text-color: chartreuse;
$gray-link: #aaa;

// Fonts
$frilly-font: "Fantasy", cursive;
$main-font: "Arial", "Helvetica", "Copperplate", sans-serif;

// Transitions
$button-slide-transition: width 2s, height 2s, background-color 2s, transform 2s;

// index.scss
@import 'reset';
@import 'variables';

@import 'Header';
@import 'Button';
@import 'Author';
@import 'Story';
@import 'Stories';
/*...*/
/*...*/

Mixins

A mixin allows you to define a set of styles that you want to reuse throughout your codebase. It also gives you the option to pass in values that make your mixin more flexible.

To use:

1. You name them with @mixin name(optional arguments) { style }.
2. To include them you use @include name(optional arguments).

SCSS

// Example
@mixin rounded-corners($radius) {
  -webkit-border-radius: $radius;
     -moz-border-radius: $radius;
      -ms-border-radius: $radius;
          border-radius: $radius;
}

@mixin centered() {
  display: flex;
  justify-content: center;
}

.box {
  @include rounded-corners(50px);
  @include centered();
}

CSS Output

.box {
  -webkit-border-radius: 50px;
  -moz-border-radius: 50px;
  -ms-border-radius: 50px;
  border-radius: 50px;
  display: flex;
  justify-content: center;
}

Colors

Sass offers built-in color functions that allow you to adjust defined color values with ease. Most of the color functions operate by manipulating a single color value - while others can be used to combine colors in different ways.

Chances are that you’ve defined most (if not all) of the colors in your project using the predefined color names from the browsers, hex codes, or RGBA. This is all well and good; however, it fails to give you the same control over your colors as when you use HSLA.

Summary

We’ve covered the basics (and more!) of Sass, but Sass can do a lot! If you’re looking for more, check out the Sass documentation for things like functions, operators, more at-rules, etc.

CSS can be messy. If you’re looking for more ways to think about organizing your styles (CSS or SASS), look into some of the modular architecture methodologies, like OOCSS, BEM or SMACSS.

Resources

• Why Sass?
• Cooler things you can do with Sass
• Downsides of using a CSS preprocessor
• How to Structure a Sass Project
• Sass to CSS Translator
• How to Organize Your CSS with a Modular Architecture