# Sass/SCSS Quick Reference

*Variables, nesting, mixins, functions, control flow*

> Source: Sass Documentation (sass-lang.com) · MIT

## Syntax

### SCSS vs Sass

```
// SCSS (superset of CSS — uses braces)
.nav { display: flex; }

// Sass (indented — no braces or semicolons)
.nav
  display: flex
```

*SCSS is the most commonly used syntax*

### Comparison

| Command | Description |
|---------|-------------|
| `SCSS (.scss)` | CSS-compatible, braces & semicolons |
| `Sass (.sass)` | Indentation-based, no braces |
| `Output` | Both compile to standard CSS |
| `Recommended` | SCSS (wider adoption, easier migration) |

## Variables

### Defining & Using

```
$primary: #3498db;
$spacing: 16px;
$font-stack: "Helvetica", Arial, sans-serif;

.btn {
  color: $primary;
  padding: $spacing;
  font-family: $font-stack;
}
```

### Variable Scope

```
$color: red;        // global
.card {
  $color: blue;     // local to .card
  color: $color;    // blue
}
.other { color: $color; } // red
```

### Flags

| Command | Description |
|---------|-------------|
| `!default` | Set only if not already defined |
| `!global` | Promote local var to global scope |

## Nesting

### Selector Nesting

```
.nav {
  ul { list-style: none; }
  li { display: inline-block; }
  a { text-decoration: none;
    &:hover { color: blue; }   // & = parent selector
  }
}
```

### Parent Selector (&)

```
.btn {
  &--primary { background: blue; }  // BEM: .btn--primary
  &__icon { margin-right: 4px; }    // BEM: .btn__icon
  .dark & { color: white; }         // .dark .btn
}
```

### Property Nesting

```
.box {
  border: { width: 1px; style: solid; color: #ccc; }
  // compiles to: border-width, border-style, border-color
}
```

## Mixins

### Define & Include

```
@mixin flex-center($direction: row) {
  display: flex;
  justify-content: center;
  align-items: center;
  flex-direction: $direction;
}

.hero { @include flex-center(column); }
```

### Content Blocks

```
@mixin responsive($breakpoint) {
  @media (min-width: $breakpoint) { @content; }
}

.sidebar {
  width: 100%;
  @include responsive(768px) { width: 300px; }
}
```

### Mixin Features

| Command | Description |
|---------|-------------|
| `@mixin name($args)` | Define reusable style block |
| `@include name()` | Use the mixin |
| `Default params` | `$arg: value` for optional params |
| `$args...` | Variable arguments (rest params) |
| `@content` | Inject caller's content block |

## Functions

### Custom Functions

```
@function rem($px, $base: 16) {
  @return math.div($px, $base) * 1rem;
}
.title { font-size: rem(24); } // 1.5rem
```

### Built-in Functions

| Command | Description |
|---------|-------------|
| `darken($color, 10%)` | Darken a color |
| `lighten($color, 10%)` | Lighten a color |
| `mix($c1, $c2, 50%)` | Mix two colors |
| `rgba($color, 0.5)` | Set alpha channel |
| `math.div($a, $b)` | Division (replaces `/`) |
| `math.round($n)` | Round number |
| `string.quote($s)` | Add quotes to string |
| `if($cond, $t, $f)` | Inline conditional |

## Extends

### Extend & Placeholder

```
%flex-center {          // placeholder — not emitted
  display: flex;
  justify-content: center;
  align-items: center;
}

.hero { @extend %flex-center; }
.modal { @extend %flex-center; }
// Both share one CSS rule via selector grouping
```

### Extend vs Mixin

| Command | Description |
|---------|-------------|
| `@extend` | Groups selectors — smaller CSS output |
| `@mixin` | Copies declarations — supports arguments |
| `% placeholder` | Extend-only (not emitted if unused) |
| `Recommendation` | Prefer mixins for parameterized styles |

## Partials & Import

### File Organization

```
// _variables.scss (partial — not compiled alone)
$primary: #3498db;

// main.scss
@use "variables";          // modern: namespaced
.btn { color: variables.$primary; }

@use "variables" as v;     // alias
.btn { color: v.$primary; }
```

### Module System

| Command | Description |
|---------|-------------|
| `@use 'file'` | Load module with namespace |
| `@use 'file' as *` | Load without namespace |
| `@use 'file' as alias` | Custom namespace |
| `@forward 'file'` | Re-export module members |
| `_partial.scss` | File not compiled independently |

*@import is deprecated — use @use and @forward instead*

## Control Flow

### Conditionals

```
@mixin theme($mode) {
  @if $mode == dark {
    background: #333; color: #fff;
  } @else {
    background: #fff; color: #333;
  }
}
```

### Loops

```
@for $i from 1 through 4 {
  .col-#{$i} { width: 25% * $i; }
}

@each $name, $color in (primary: blue, danger: red) {
  .text-#{$name} { color: $color; }
}
```

### Directives

| Command | Description |
|---------|-------------|
| `@if / @else if / @else` | Conditional logic |
| `@for $i from a through b` | Numeric loop (inclusive) |
| `@for $i from a to b` | Numeric loop (exclusive end) |
| `@each $item in $list` | Iterate list or map |
| `@while` | Loop while condition is true |
| `#{$var}` | Interpolation in selectors/props |

## Maps & Lists

### Maps

```
$colors: (primary: #3498db, danger: #e74c3c, success: #2ecc71);

.alert { color: map.get($colors, danger); }

@each $name, $color in $colors {
  .bg-#{$name} { background: $color; }
}
```

### Lists

```
$sizes: 8px 16px 24px 32px;
.box { padding: list.nth($sizes, 2); } // 16px
```

### Map & List Functions

| Command | Description |
|---------|-------------|
| `map.get($map, $key)` | Get value by key |
| `map.merge($m1, $m2)` | Merge two maps |
| `map.keys($map)` | List of all keys |
| `map.has-key($map, $key)` | Check if key exists |
| `list.nth($list, $n)` | Get item at index (1-based) |
| `list.length($list)` | Number of items |
| `list.append($list, $val)` | Add item to list |

## Common Patterns

### Responsive Breakpoints

```
$breakpoints: (sm: 576px, md: 768px, lg: 992px, xl: 1200px);

@mixin bp($name) {
  @media (min-width: map.get($breakpoints, $name)) {
    @content;
  }
}
.sidebar { width: 100%; @include bp(md) { width: 300px; } }
```

### Utility Generator

```
$spaces: (0: 0, 1: 4px, 2: 8px, 3: 16px, 4: 32px);
@each $key, $val in $spaces {
  .mt-#{$key} { margin-top: $val; }
  .mb-#{$key} { margin-bottom: $val; }
  .p-#{$key} { padding: $val; }
}
```

### Dark Mode

```
@mixin dark { @media (prefers-color-scheme: dark) { @content; } }
body {
  background: #fff;
  @include dark { background: #1a1a1a; color: #eee; }
}
```