A guide to writing CSS, the language that controls the appearance and layout of web pages. It focuses on standard CSS, accessibility, speed, clear structure, and code that remains easy to maintain.

Use it when writing, reviewing, or restructuring CSS, especially when choosing native CSS features, supporting motion and contrast preferences, or improving selectors and shared values.

It helps prevent styles from making websites harder to use with assistive technology, slower to render, or difficult to change later. It also provides patterns and snippets for common styling work.

css-coder — Skill for Claude Code and Codex by schalkneethling

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.

Any agent

npx skills add schalkneethling/webdev-agent-skills --skill css-coder

Clone the repo

git clone --depth 1 https://github.com/schalkneethling/webdev-agent-skills

Made for: Claude Code, Codex.

Wrote this? Show the measurements

A badge with what this costs and how it scanned, read live from this page, so it follows the numbers instead of freezing them. Markdown for a README, HTML for a documentation site or a project page.

README.md

[![agentmods](https://agentmods.dev/badge/skills/schalkneethling/webdev-agent-skills/css-coder/github.svg)](https://agentmods.dev/skills/schalkneethling/webdev-agent-skills/css-coder)

Your own site

<a href="https://agentmods.dev/skills/schalkneethling/webdev-agent-skills/css-coder"><img src="https://agentmods.dev/badge/skills/schalkneethling/webdev-agent-skills/css-coder/github.svg" alt="Measured on agentmods" height="20"></a>

Or the 80×15 button, for a site that already has a row of RSS and ATOM ones. Only the verdict fits; the numbers stay here.

Your own site · 80×15

<a href="https://agentmods.dev/skills/schalkneethling/webdev-agent-skills/css-coder"><img src="https://agentmods.dev/badge/skills/schalkneethling/webdev-agent-skills/css-coder.svg" alt="Reviewed on agentmods" width="80" height="20"></a>

Per session 63 Skills are progressive disclosure: only the name and description are preloaded; the body loads when the skill is used.

When invoked 979 The whole file, excluding the scripts and references it only reads on demand.

Security scan A 0 findings. A grade says what 26 rules found in the file — not that it is safe.

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.

Model	Per session	Once invoked
Fable 5.1	$0.00063	$0.00979
Opus 5.5	$0.00025	$0.00392
Sonnet 5.5	$0.00013	$0.00196
Haiku 4.5	$0.00006	$0.00098

Measured 2mo ago against content hash baf87ae9afa4, method: parsed. Prices are Anthropic first-party input rates as of 2026-10-07, from the pricing page.

Security

Grade A, and why

css-coder 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 2mo 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.

css-coder/SKILL.md · 96 lines

How it starts

The opening of the file, as written. The whole thing — 96 lines — stays where its author put it; the contents beside it link to each section on GitHub.

CSS Coder

Guidance for writing CSS that prioritizes web standards, accessibility, performance, and maintainability.

Core Principles

Web standards first — Use native CSS features before reaching for libraries or frameworks. No Tailwind, no CSS-in-JS unless explicitly requested.
Accessibility as a requirement — Ensure styles support, never hinder, assistive technologies. Respect user preferences (motion, color scheme, contrast).
Performance matters — Minimize repaints, avoid layout thrashing, use efficient selectors.
Readable over clever — Future maintainers (including the author) should understand the code at a glance.
Explicit over implicit — Avoid magic numbers and unexplained values. Use custom properties for shared values.

Workflow

Check references first — Before writing CSS, consult references/patterns.md for established patterns and snippets.
Validate against specs — When uncertain, reference MDN Web Docs or CSS specifications.
Suggest alternatives — Offer ideas beyond the skill's patterns when appropriate, but always aligned with the core principles above.

Writing Guidelines

Selectors

Prefer class selectors over element or ID selectors for styling.
Keep specificity low and predictable.
Avoid deep nesting (aim for 2-3 levels maximum).

Custom Properties

Use -- prefixed custom properties for colors, spacing, typography, and other repeated values.
Define at :root or appropriate scope.
Name descriptively: --color-primary, --spacing-md, --font-size-body.

Logical Properties

Always use logical properties (margin-inline, padding-block, inset-inline-start, block-size, etc.) instead of physical properties (margin-left, padding-top, left, height, etc.).
Logical properties support internationalization and different writing modes automatically.
Only fall back to physical properties where logical equivalents do not yet exist.

Units

Use rem for typography and spacing (respects user font-size preferences).
Use em for component-relative sizing when appropriate.
Use viewport units (vw, vh, dvh) thoughtfully, with fallbacks where needed.
Avoid px for font sizes; acceptable for borders, shadows, and fine details.

Read the full file on GitHub · 96 lines

Files

What ships with it

1 file beside SKILL.md in the same directory: the scripts, references and assets a skill reads on demand. Not counted in the per-session cost; read them before you install if any of them is executable.

references/patterns.md 4.6 KB

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.

2mo ago First seen · 96 lines · 63 tokens per session scan A baf87ae9afa4

Subscribe to this mod's changes

css-coder is a skill published in the GitHub repository schalkneethling/webdev-agent-skills (7 stars, last pushed 6mo ago), licensed MIT. It adds 63 tokens to every session and 979 once invoked, about $0.0003 per session on Opus 5.5. 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 2026-08-31.

CSS and styling Frontend

css-coder next to 6 skills from other repositories
Mod	Type	Stars	Last push	Licence	Scan	Tokens	Works with
css-coderschalkneethling/webdev-agent-skills	Skill	7	6mo ago	MIT	A	63	Claude Code, Codex
anti-slop-designsickn33/agentic-awesome-skills	Skill	49k	yesterday	MIT	A	34	Claude Code
chakra-ui-builderchakra-ui/chakra-ui	Skill	41k	yesterday	MIT	A	214	Claude Code, Codex
visual-ralphYeachan-Heo/oh-my-codex	Skill	34k	4d ago	MIT	A	52	Codex
open-design-setupcompozy/compozy	Skill	2.8k	yesterday	MIT	A	67	Claude Code, Codex
edit-sitemicrosoft/power-platform-skills	Skill	1.1k	yesterday	MIT	A	104	Claude Code
frontend-visual-qadaymade/claude-code-skills	Skill	1.5k	yesterday	MIT	A	125	Claude Code, Codex