scss-best-practices

SKILL.md

SCSS Best Practices

You are an expert in SCSS (Sassy CSS), CSS architecture, and maintainable stylesheet development.

Key Principles

Write modular, reusable SCSS that scales with project complexity

Follow the DRY (Don't Repeat Yourself) principle using variables, mixins, and functions

Maintain clear separation between structure, skin, and state styles

Prioritize readability and maintainability over clever abstractions

File Organization
Architecture Pattern (7-1 Pattern)

scss/
├── abstracts/
│   ├── _variables.scss    # Global variables
│   ├── _functions.scss    # SCSS functions
│   ├── _mixins.scss       # Reusable mixins
│   └── _placeholders.scss # Extendable placeholders
├── base/
│   ├── _reset.scss        # CSS reset/normalize
│   ├── _typography.scss   # Typography rules
│   └── _base.scss         # Base element styles
├── components/
│   ├── _buttons.scss      # Button components
│   ├── _cards.scss        # Card components
│   └── _forms.scss        # Form components
├── layout/
│   ├── _header.scss       # Header layout
│   ├── _footer.scss       # Footer layout
│   ├── _grid.scss         # Grid system
│   └── _navigation.scss   # Navigation layout
├── pages/
│   ├── _home.scss         # Home page specific
│   └── _contact.scss      # Contact page specific
├── themes/
│   └── _default.scss      # Default theme
├── vendors/
│   └── _bootstrap.scss    # Third-party overrides
└── main.scss              # Main manifest file

Import Order

// main.scss
@use 'abstracts/variables';
@use 'abstracts/functions';
@use 'abstracts/mixins';
@use 'abstracts/placeholders';

@use 'vendors/normalize';

@use 'base/reset';
@use 'base/typography';
@use 'base/base';

@use 'layout/grid';
@use 'layout/header';
@use 'layout/navigation';
@use 'layout/footer';

@use 'components/buttons';
@use 'components/cards';
@use 'components/forms';

@use 'pages/home';

@use 'themes/default';

Variables

Naming Convention

// Use semantic, descriptive names
// Format: $category-property-variant

// Colors
$color-primary: #3498db;
$color-primary-light: lighten($color-primary, 15%);
$color-primary-dark: darken($color-primary, 15%);
$color-secondary: #2ecc71;
$color-text: #333333;
$color-text-muted: #666666;
$color-background: #ffffff;
$color-border: #e0e0e0;
$color-error: #e74c3c;
$color-success: #27ae60;
$color-warning: #f39c12;

// Typography
$font-family-base: 'Helvetica Neue', Arial, sans-serif;
$font-family-heading: 'Georgia', serif;
$font-size-base: 1rem;
$font-size-small: 0.875rem;
$font-size-large: 1.25rem;
$font-weight-normal: 400;
$font-weight-bold: 700;
$line-height-base: 1.5;

// Spacing (use consistent scale)
$spacing-unit: 8px;
$spacing-xs: $spacing-unit * 0.5;  // 4px
$spacing-sm: $spacing-unit;        // 8px
$spacing-md: $spacing-unit * 2;    // 16px
$spacing-lg: $spacing-unit * 3;    // 24px
$spacing-xl: $spacing-unit * 4;    // 32px
$spacing-xxl: $spacing-unit * 6;   // 48px

// Breakpoints
$breakpoint-sm: 576px;
$breakpoint-md: 768px;
$breakpoint-lg: 992px;
$breakpoint-xl: 1200px;
$breakpoint-xxl: 1400px;

// Z-index scale
$z-index-dropdown: 1000;
$z-index-sticky: 1020;
$z-index-fixed: 1030;
$z-index-modal-backdrop: 1040;
$z-index-modal: 1050;
$z-index-popover: 1060;
$z-index-tooltip: 1070;

// Transitions
$transition-base: 0.3s ease;
$transition-fast: 0.15s ease;
$transition-slow: 0.5s ease;

// Border radius
$border-radius-sm: 2px;
$border-radius-md: 4px;
$border-radius-lg: 8px;
$border-radius-pill: 50px;
$border-radius-circle: 50%;

// Shadows
$shadow-sm: 0 1px 2px rgba(0, 0, 0, 0.05);
$shadow-md: 0 4px 6px rgba(0, 0, 0, 0.1);
$shadow-lg: 0 10px 15px rgba(0, 0, 0, 0.1);
$shadow-xl: 0 20px 25px rgba(0, 0, 0, 0.15);

Maps for Related Values

// Use maps for grouped values
$colors: (
  'primary': #3498db,
  'secondary': #2ecc71,
  'danger': #e74c3c,
  'warning': #f39c12,
  'info': #17a2b8,
  'success': #27ae60
);

$breakpoints: (
  'sm': 576px,
  'md': 768px,
  'lg': 992px,
  'xl': 1200px,
  'xxl': 1400px
);

// Access with map-get
.element {
  color: map-get($colors, 'primary');
}

Mixins

Responsive Breakpoints

@mixin respond-to($breakpoint) {
  @if map-has-key($breakpoints, $breakpoint) {
    @media (min-width: map-get($breakpoints, $breakpoint)) {
      @content;
    }
  } @else {
    @warn "Unknown breakpoint: #{$breakpoint}";
  }
}

// Usage
.element {
  width: 100%;

  @include respond-to('md') {
    width: 50%;
  }

  @include respond-to('lg') {
    width: 33.333%;
  }
}

Flexbox Utilities

@mixin flex-center {
  display: flex;
  align-items: center;
  justify-content: center;
}

@mixin flex-between {
  display: flex;
  align-items: center;
  justify-content: space-between;
}

@mixin flex-column {
  display: flex;
  flex-direction: column;
}

Typography

@mixin font-size($size, $line-height: null) {
  font-size: $size;
  @if $line-height {
    line-height: $line-height;
  }
}

@mixin truncate($lines: 1) {
  @if $lines == 1 {
    white-space: nowrap;
    overflow: hidden;
    text-overflow: ellipsis;
  } @else {
    display: -webkit-box;
    -webkit-line-clamp: $lines;
    -webkit-box-orient: vertical;
    overflow: hidden;
  }
}

Accessibility

@mixin visually-hidden {
  position: absolute;
  width: 1px;
  height: 1px;
  padding: 0;
  margin: -1px;
  overflow: hidden;
  clip: rect(0, 0, 0, 0);
  white-space: nowrap;
  border: 0;
}

@mixin focus-visible {
  &:focus-visible {
    outline: 2px solid $color-primary;
    outline-offset: 2px;
  }
}

BEM Naming Convention

Structure

// Block: Standalone component
// Element: Part of block (block__element)
// Modifier: Variant (block--modifier or block__element--modifier)

.card {
  // Block styles
  background: $color-background;
  border-radius: $border-radius-md;
  box-shadow: $shadow-md;

  // Element
  &__header {
    padding: $spacing-md;
    border-bottom: 1px solid $color-border;
  }

  &__title {
    margin: 0;
    font-size: $font-size-large;
    font-weight: $font-weight-bold;
  }

  &__body {
    padding: $spacing-md;
  }

  &__footer {
    padding: $spacing-md;
    border-top: 1px solid $color-border;
  }

  // Modifier
  &--featured {
    border: 2px solid $color-primary;
  }

  &--compact {
    .card__header,
    .card__body,
    .card__footer {
      padding: $spacing-sm;
    }
  }
}

Nesting Rules

Maximum Nesting Depth

// BAD: Too deep nesting
.nav {
  .nav-list {
    .nav-item {
      .nav-link {
        .nav-icon {
          // 5 levels deep - avoid this
        }
      }
    }
  }
}

// GOOD: Keep nesting to 3 levels maximum
.nav {
  // Level 1
}

.nav__list {
  // Level 1
}

.nav__item {
  // Level 1
}

.nav__link {
  color: $color-text;

  &:hover,
  &:focus {
    // Level 2 - acceptable for states
    color: $color-primary;
  }

  &--active {
    // Level 2 - acceptable for modifiers
    color: $color-primary;
    font-weight: $font-weight-bold;
  }
}

Acceptable Nesting

.component {
  // Direct child pseudo-elements
  &::before,
  &::after {
    content: '';
  }

  // State modifiers
  &:hover,
  &:focus,
  &:active {
    // State styles
  }

  // BEM modifiers
  &--variant {
    // Modifier styles
  }

  // Media queries
  @include respond-to('md') {
    // Responsive styles
  }
}

Functions

Color Functions

@function tint($color, $percentage) {
  @return mix(white, $color, $percentage);
}

@function shade($color, $percentage) {
  @return mix(black, $color, $percentage);
}

// Usage
.element {
  background: tint($color-primary, 20%);
  border-color: shade($color-primary, 10%);
}

Unit Conversion

@function px-to-rem($px, $base: 16) {
  @return ($px / $base) * 1rem;
}

@function rem-to-px($rem, $base: 16) {
  @return ($rem / 1rem) * $base * 1px;
}

// Usage
.element {
  font-size: px-to-rem(18); // 1.125rem
  padding: px-to-rem(24);   // 1.5rem
}

Spacing Function

@function spacing($multiplier) {
  @return $spacing-unit * $multiplier;
}

// Usage
.element {
  margin-bottom: spacing(2); // 16px
  padding: spacing(3);       // 24px
}

Extend and Placeholders

Use Placeholders Over Classes

// Define placeholder
%button-base {
  display: inline-flex;
  align-items: center;
  justify-content: center;
  padding: $spacing-sm $spacing-md;
  border: none;
  border-radius: $border-radius-md;
  font-family: inherit;
  font-size: $font-size-base;
  font-weight: $font-weight-bold;
  text-decoration: none;
  cursor: pointer;
  transition: all $transition-base;

  &:disabled {
    opacity: 0.5;
    cursor: not-allowed;
  }
}

// Extend placeholder
.btn-primary {
  @extend %button-base;
  background: $color-primary;
  color: white;

  &:hover:not(:disabled) {
    background: darken($color-primary, 10%);
  }
}

.btn-secondary {
  @extend %button-base;
  background: transparent;
  color: $color-primary;
  border: 2px solid $color-primary;

  &:hover:not(:disabled) {
    background: $color-primary;
    color: white;
  }
}

Loops and Iteration

Generate Utility Classes

// Spacing utilities
$spacing-directions: (
  '': '',
  't': '-top',
  'r': '-right',
  'b': '-bottom',
  'l': '-left',
  'x': '-inline',
  'y': '-block'
);

@each $abbr, $direction in $spacing-directions {
  @for $i from 0 through 8 {
    .m#{$abbr}-#{$i} {
      margin#{$direction}: spacing($i);
    }
    .p#{$abbr}-#{$i} {
      padding#{$direction}: spacing($i);
    }
  }
}

// Color utilities
@each $name, $color in $colors {
  .text-#{$name} {
    color: $color;
  }
  .bg-#{$name} {
    background-color: $color;
  }
  .border-#{$name} {
    border-color: $color;
  }
}

Performance Best Practices

Avoid overly specific selectors; aim for specificity of 0-1-0 (single class)

Never use !important except for utility classes

Minimize use of @extend across files (can cause bloat)

Use @use and @forward instead of @import (deprecated)

Compile with source maps in development, without in production

Use autoprefixer for vendor prefixes instead of manual prefixes

Modern SCSS Features

Module System

// _variables.scss
$primary: #3498db;

// _mixins.scss
@use 'variables' as vars;

@mixin themed-button {
  background: vars.$primary;
}

// main.scss
@use 'mixins';

.button {
  @include mixins.themed-button;
}

Built-in Modules

@use 'sass:math';
@use 'sass:color';
@use 'sass:list';
@use 'sass:map';
@use 'sass:string';

.element {
  width: math.div(100%, 3);
  background: color.adjust($color-primary, $lightness: 10%);
}

Code Style

Use 2 spaces for indentation

Use single quotes for strings

Add a space after colons in declarations

Add a space before opening braces

Put closing braces on new lines

Separate rule sets with blank lines

Order properties logically (positioning, box model, typography, visual, misc)

Comment complex calculations and non-obvious code