CSS Standards

Apply these standards when writing or reviewing CSS, SCSS, or SASS code to ensure maintainability and performance.

Structure and Organization

1. Ordering and Grouping Styles

Group related styles together in this order:

.component { /* Layout */ position: relative; display: flex;

/* Box model */
margin: 10px;
padding: 20px;
border: 1px solid #ccc;

/* Visual */
background-color: #f5f5f5;
color: #333;

/* Typography */
font-size: 16px;
line-height: 1.5;

/* Misc */
cursor: pointer;

}

Use CSS Stylelint to enforce consistent rule order.

2. Modular CSS

• Split CSS into smaller modules (buttons.css , typography.css )

• Name files after components (Button.module.css , Header.module.css )

• Use scoped styles in Vue/React/Svelte single-file components

• In Angular, use styleUrls property for component styles

3. CSS Reset

Use a base reset or Normalize.css for consistent cross-browser behavior.

4. Comment Styles Clearly

/* Reusable Components */ .button { ... }

/* Page-Specific Styles */ .homepage-header { ... }

Selectors and Specificity

5. Minimize Selector Nesting

❌ Bad:

.header .nav ul li a { color: #fff; }

✅ Better:

.nav-link { color: #fff; }

6. Limit Specificity

Avoid IDs and overly specific selectors. Prefer classes.

❌ Bad:

#header p.intro-text { font-size: 16px; }

✅ Better:

.intro-text { font-size: 16px; }

7. Use Short Selectors for Components

.btn { ... } /* Consistent button naming / .card { ... } / Clear content card name / .nav-link { ... } / Descriptive navigation link */

Efficient Reuse

8. CSS Variables

:root { --primary-color: #007bff; --secondary-color: #6c757d; --font-size-base: 16px; --spacing-sm: 8px; --spacing-md: 16px; --spacing-lg: 24px; }

body { color: var(--primary-color); font-size: var(--font-size-base); }

9. Reusable Utility Classes

.text-center { text-align: center; }

.margin-bottom-sm { margin-bottom: var(--spacing-sm); }

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

10. Component-Based Styles

Avoid global element selectors.

❌ Bad:

h1 { font-size: 24px; }

✅ Better:

.card-title { font-size: 24px; }

Performance and Maintainability

11. Avoid Inline Styles

❌ Bad:

<div style="color: red; font-size: 20px;">Content</div>

✅ Better:

<div class="error-text">Content</div>

.error-text { color: red; font-size: 20px; }

12. Minimize !important

Use !important only as a last resort. Excessive use makes maintenance difficult.

13. Optimize for Production

• Use PostCSS or build tools to minify CSS

• Remove unused CSS with tools like PurgeCSS

• Combine and optimize stylesheets

14. Limit Complex Animations

Excessive or complex CSS animations can hurt performance. Test on low-end devices.

Responsiveness

15. Media Queries

/* Base (mobile-first) */ .container { width: 100%; padding: var(--spacing-md); }

/* Tablet */ @media screen and (width >= 768px) { .container { width: 95%; padding: var(--spacing-lg); } }

/* Desktop */ @media screen and (width >= 1024px) { .container { width: 80%; max-width: 1200px; } }

16. Responsive Units

Use flexible units instead of fixed pixels.

body { font-size: 1rem; /* Scalable base */ line-height: 1.5; }

.container { width: 90%; /* Flexible width / max-width: 1200px; margin: 0 auto; padding: 2rem; / Scalable spacing */ }

Code Cleanliness

17. Consistent Indentation

Use 2 or 4 spaces consistently. Use Prettier or Stylelint for enforcement.

18. Remove Unused CSS

Use PurgeCSS or similar tools to remove unused styles in production.

19. Avoid Redundancy

❌ Bad:

p { font-size: 16px; font-size: 16px; /* Duplicate */ }

✅ Better:

p { font-size: 16px; }

Example: Well-Structured Component

/* Card Component / .card { / Layout */ display: flex; flex-direction: column;

/* Box model */
padding: var(--spacing-lg);
border: 1px solid var(--border-color);
border-radius: 8px;

/* Visual */
background-color: var(--card-bg);
box-shadow: 0 2px 4px rgba(0, 0, 0, 0.1);

/* Misc */
transition: transform 0.2s ease;

}

.card:hover { transform: translateY(-4px); box-shadow: 0 4px 8px rgba(0, 0, 0, 0.15); }

.card-title { /* Typography */ font-size: 1.5rem; font-weight: 600; color: var(--text-primary);

/* Box model */
margin-bottom: var(--spacing-sm);

}

.card-content { /* Typography */ font-size: 1rem; line-height: 1.6; color: var(--text-secondary); }

/* Responsive adjustments */ @media screen and (width >= 768px) { .card { flex-direction: row; padding: var(--spacing-xl); } }

When to Apply

Apply these standards when:

• Creating new stylesheets

• Writing component styles

• Refactoring existing CSS

• Reviewing CSS code

• Setting up CSS architecture

• Working with CSS preprocessors (SCSS, SASS)

• User asks about CSS best practices