css

A set of coding guidelines for CSS, the language that controls how web pages look and are laid out. It recommends organizing styles into focused, reusable files and considering performance and accessibility.

In plain words
What is it for?
Use it when structuring styles for web pages and components, including base styles, layouts, utilities, Sass files, buttons, and cards.
Why use it?
It helps prevent large, tangled stylesheets that are difficult to change and can lead to inconsistent or inaccessible interfaces.

Cursor rule

Install

Getting it into your agent

One page per mod, every tool's command on it. A separate URL per tool would split the same page into five that compete with each other.

agentmods
npx agentmods add rules/sanjeed5/awesome-cursor-rules-mdc/css
Clone the repo
git clone --depth 1 https://github.com/sanjeed5/awesome-cursor-rules-mdc
Per session 2,561 This file is loaded in full into every session.
When invoked 2,561 The same file — it is already loaded in full.
Security scan A 0 findings. Scan, not verified.
Origin original No closer match found in the catalogue.
Token cost

What it costs to keep this loaded

Counted locally with the o200k_base tokenizer, which is exact for GPT models; Claude uses its own tokenizer and its counts differ. Treat this as one consistent yardstick across the catalogue rather than a bill. Prices are per million input tokens.

ModelPer sessionOnce invoked
Fable 5 $0.02561 $0.02561
Opus 5 $0.01281 $0.01281
Sonnet 5 $0.00512 $0.00512
Haiku 4.5 $0.00256 $0.00256

Measured 2d ago against content hash b2e5ddbdaef2, method: parsed. Prices are Anthropic first-party input rates as of 2026-08-30, from the pricing page.

Security

Grade A, and why

css scanned grade A with 0 findings against 26 rules in 11 categories — prompt injection, anti-refusal, data exfiltration, privilege escalation, supply chain, agent snooping, system-prompt leakage, SSRF and excessive agency — measured 2d ago.

A static scan of the body, not an audit. Every finding is printed with the line that produced it so you can judge whether it matters here. A mod is markdown that instructs an agent; that is exactly why what it instructs is worth reading.

Nothing flagged

None of the 26 patterns this scan looks for appear in this file: no shell pipes, no recursive deletes, no credential paths, no hidden text, no instruction-override or anti-refusal phrasing, no agent-config snooping. That is not a guarantee, it is the absence of the things that are checkable.

rules-mdc/css.mdc · 429 lines

How it starts

The opening of the file, as written. The whole thing — 429 lines — stays where its author put it; the contents beside it link to each section on GitHub.

CSS Best Practices

This guide outlines the definitive best practices for writing CSS within our team. Adhering to these principles ensures our stylesheets are scalable, maintainable, performant, and accessible.

1. Code Organization & Structure

Adopt a modular, predictable structure. Use Sass for pre-processing.

1.1 File Structure (Modular & Scalable)

Organize CSS into logical, focused files. A simplified ITCSS-like structure is recommended.

/*
  css/
  ├── base/             // Project-wide defaults (reset, typography, variables)
  │   ├── _reset.scss
  │   ├── _typography.scss
  │   └── _variables.scss // Design tokens
  ├── components/       // Self-contained UI components (buttons, cards)
  │   ├── _button.scss
  │   └── _card.scss
  ├── layout/           // Major page sections (header, footer, grid)
  │   ├── _grid.scss
  │   └── _header.scss
  └── utilities/        // Single-purpose helper classes (spacing, text alignment)
      ├── _spacing.scss
      └── _helpers.scss
*/

// main.scss
@import 'base/reset';
@import 'base/variables';
@import 'base/typography';

@import 'layout/grid';
@import 'layout/header';

@import 'components/button';
@import 'components/card';

@import 'utilities/spacing';
@import 'utilities/helpers';

1.2 Naming Convention (BEM)

Use BEM (Block-Element-Modifier) for clear, flat, and highly readable selectors. This prevents specificity wars and improves reusability.

❌ BAD: Deeply nested, ambiguous selectors

.header .nav ul li a { /* ... */ }
.card.featured { /* ... */ }

✅ GOOD: BEM for clarity and reusability

/* Block */
.card { /* ... */ }

/* Element */
.card__title { /* ... */ }
.card__image { /* ... */ }

/* Modifier */
.card--featured { /* ... */ }
.card__title--large { /* ... */ }

1.3 CSS Custom Properties (Design Tokens)

Centralize design values (colors, fonts, spacing) using CSS variables. This enables consistency, easy theming, and dynamic updates.

/* _variables.scss */
:root {
  --color-primary: #007bff;
  --color-text: #333;
  --font-family-sans: -apple-system, BlinkMacSystemFont, "Segoe UI", Roboto;
  --spacing-md: 1rem;
}

/* Usage */
.button {
  background-color: var(--color-primary);
  color: white;
  padding: var(--spacing-md);
  font-family: var(--font-family-sans);
}

Read the full file on GitHub · 429 lines

Changes

What this file has done since we first saw it

Hashed on every crawl. A supply-chain change to an agent config is a question of when, not whether, so the history is kept rather than the latest state alone.

  1. 2d ago First seen · 429 lines · 0 tokens per session scan A b2e5ddbdaef2

Subscribe to this mod's changes

css is a cursor rule published in the GitHub repository sanjeed5/awesome-cursor-rules-mdc (3,570 stars, last pushed 3mo ago), licensed CC0-1.0. It adds 2,561 tokens to every session, about $0.0128 per session on Opus 5. A static security scan graded it A with 0 findings. No closer match exists in the catalogue, so it is treated as the original; first seen 2026-08-30.