angular-css-bem-best-practices（Angular CSS BEM 最佳实践）

Angular + BEM CSS Best Practices

A methodology guide for combining Angular's component architecture with BEM (Block Element Modifier) CSS naming convention to create reusable components and enable code sharing in front-end development. Contains 6 rules with bad/good examples in CSS, SCSS, and SASS.

When to Apply

Reference these guidelines when:

• Writing CSS/SCSS/SASS for Angular components
• Naming CSS classes in Angular templates
• Reviewing component styles for consistency
• Deciding whether to split a component based on styling complexity
• Setting up CSS architecture for a new Angular project
• Refactoring existing styles to follow BEM methodology

Core Principles

• 1 Component = 1 BEM Block — The block name matches the component selector
• Max 2 Levels — Only Block and Block__Element, never Block__Element__SubElement
• Split When Deep — If you need a third level, extract a child component
• Flat Selectors — No descendant, child, or tag-qualified selectors
• Semantic Names — Element names describe *what*, not *how* or *where*
• Modifiers for Variants — Use --modifier for states and variants, always with the base class

Rule Categories by Priority

Quick Reference

1. Block = Component Selector (CRITICAL)

• bem-block-selector - BEM block name must match the Angular component selector (minus prefix)

2. Maximum 2 Levels (CRITICAL)

• bem-max-nesting - Never nest beyond .block__element — no .block__element__subelement

3. Split Child Components (CRITICAL)

• bem-split-components - Extract child components when BEM depth would exceed 2 levels

4. Element Naming (HIGH)

• bem-element-naming - Use semantic, descriptive kebab-case names for BEM elements

5. Modifier Patterns (HIGH)

• bem-modifier-patterns - Use --modifier correctly for states and variants with Angular class bindings

6. No Cascading (HIGH)

• bem-no-cascading - Avoid descendant, child, and tag-qualified selectors — keep BEM flat

BEM Cheat Sheet

.block                    → Component root (matches selector)
.block__element           → Child part of the component
.block--modifier          → Variant of the entire block
.block__element--modifier → Variant of a single element

✅ .user-card
✅ .user-card__avatar
✅ .user-card--featured
✅ .user-card__name--highlighted

❌ .user-card__header__title       (3 levels)
❌ .user-card .user-card__avatar   (descendant selector)
❌ div.user-card                   (tag-qualified)

How to Use

Read individual rule files for detailed explanations and code examples:

rules/bem-block-selector.md
rules/bem-max-nesting.md
rules/bem-split-components.md
rules/bem-element-naming.md
rules/bem-modifier-patterns.md
rules/bem-no-cascading.md

Each rule file contains:

• Brief explanation of why it matters
• Incorrect code examples (CSS, SCSS, SASS)
• Correct code examples (CSS, SCSS, SASS)
• Angular component integration patterns
• Summary table and references

Full Compiled Document

For the complete guide with all rules expanded: AGENTS.md