BEM Methodology with SCSS

BEM Basics

Understanding the core concepts of BEM: Blocks, Elements, and Modifiers.

// BEM Naming Convention
.block {}                    // Block
.block__element {}          // Element
.block--modifier {}         // Block Modifier
.block__element--modifier {} // Element Modifier

// Example with a card component
.card {}                    // Block
.card__header {}           // Element
.card__content {}          // Element
.card__footer {}           // Element
.card--featured {}         // Modifier
.card__header--highlighted {} // Element Modifier

HTML Usage:

<div class="card card--featured">
    <div class="card__header card__header--highlighted">
        <h2 class="card__title">Title</h2>
    </div>
    <div class="card__content">Content</div>
    <div class="card__footer">Footer</div>
</div>

BEM with SCSS Nesting

Using SCSS nesting to write BEM in a more maintainable way.

// Traditional CSS
.button {}
.button__icon {}
.button__text {}
.button--primary {}
.button--primary__icon {}

// SCSS with nesting
.button {
    // Block styles
    display: inline-flex;
    align-items: center;
    padding: 0.5rem 1rem;
    
    // Elements
    &__icon {
        margin-right: 0.5rem;
    }
    
    &__text {
        font-weight: 500;
    }
    
    // Modifiers
    &--primary {
        background: blue;
        color: white;
        
        // Modifier-specific element styles
        .button__icon {
            // or use &__icon for better nesting
            fill: white;
        }
    }
}

BEM Mixins

Creating reusable mixins for BEM patterns.

// BEM Mixins
@mixin block($block) {
    .#{$block} {
        @content;
    }
}

@mixin element($element) {
    &__#{$element} {
        @content;
    }
}

@mixin modifier($modifier) {
    &--#{$modifier} {
        @content;
    }
}

// Usage
@include block('nav') {
    display: flex;
    
    @include element('item') {
        padding: 1rem;
        
        @include modifier('active') {
            font-weight: bold;
        }
    }
    
    @include modifier('vertical') {
        flex-direction: column;
    }
}

// Outputs
.nav {
    display: flex;
}
.nav__item {
    padding: 1rem;
}
.nav__item--active {
    font-weight: bold;
}
.nav--vertical {
    flex-direction: column;
}

Complex Components

Handling complex components with nested elements and modifiers.

// Complex form component
.form {
    &__group {
        margin-bottom: 1rem;
        
        &--error {
            .form__label {
                color: red;
            }
            
            .form__input {
                border-color: red;
            }
        }
    }
    
    &__label {
        display: block;
        margin-bottom: 0.5rem;
        
        &--required {
            &::after {
                content: "*";
                color: red;
            }
        }
    }
    
    &__input {
        width: 100%;
        padding: 0.5rem;
        
        &--large {
            padding: 1rem;
        }
        
        &--error {
            border-color: red;
        }
    }
    
    &--inline {
        .form__group {
            display: flex;
            align-items: center;
        }
        
        .form__label {
            margin-bottom: 0;
            margin-right: 1rem;
        }
    }
}

HTML Usage:

<form class="form form--inline">
    <div class="form__group form__group--error">
        <label class="form__label form__label--required">
            Username
        </label>
        <input class="form__input form__input--large">
    </div>
</form>

Context and Dependency Management

Handling component context and dependencies while maintaining BEM principles.

// Managing context
.article {
    &__header {
        margin-bottom: 2rem;
    }
    
    // Context-based styling
    .button {
        margin-right: 1rem;
        
        &:last-child {
            margin-right: 0;
        }
    }
}

// Component dependencies
.modal {
    &__content {
        .form {
            margin-bottom: 0;  // Override default form margin
        }
    }
}

// Theme variations
.theme-dark {
    .button {
        &--primary {
            background: lighten($primary-color, 10%);
        }
    }
}

BEM Best Practices

Naming Conventions

Use meaningful and clear names for blocks
Keep element and modifier names concise
Use double underscores for elements (__)
Use double hyphens for modifiers (--)
Avoid excessive nesting of elements

Structure

Keep blocks independent and self-contained
Avoid deep nesting of elements (max 2 levels)
Use mixins for repeated patterns
Maintain a flat structure where possible

Modifiers

Use boolean modifiers when appropriate (--disabled, --active)
Use key-value modifiers for variants (--color-primary, --size-large)
Keep modifier names consistent across components
Avoid modifier-only classes without their block class