A guide for converting flat CSS selectors into nested CSS while keeping style checks satisfied. CSS nesting lets related selectors be written inside one another, and specificity describes how strongly a selector targets an element.

Use it when nesting CSS with the ampersand selector, fixing descending-specificity errors, or restructuring CSS without creating duplicate resolved selectors.

It helps avoid selector-order conflicts and duplicate selectors that can make styles fail lint checks or behave unexpectedly after a refactor.

css-nesting — Skill for Claude Code by fubits1/svelte-skills

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 fubits1/svelte-skills --skill css-nesting

Clone the repo

git clone --depth 1 https://github.com/fubits1/svelte-skills

Made for: Claude Code.

Or install frontend, the plugin that ships this one along with the rest of its 13 skills.

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/fubits1/svelte-skills/css-nesting/github.svg)](https://agentmods.dev/skills/fubits1/svelte-skills/css-nesting)

Your own site

<a href="https://agentmods.dev/skills/fubits1/svelte-skills/css-nesting"><img src="https://agentmods.dev/badge/skills/fubits1/svelte-skills/css-nesting/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/fubits1/svelte-skills/css-nesting"><img src="https://agentmods.dev/badge/skills/fubits1/svelte-skills/css-nesting.svg" alt="Reviewed on agentmods" width="80" height="20"></a>

Per session 51 Skills are progressive disclosure: only the name and description are preloaded; the body loads when the skill is used.

When invoked 1,760 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	$0.00051	$0.01760
Opus 5.5	$0.00020	$0.00704
Sonnet 5.5	$0.00010	$0.00352
Haiku 4.5	$0.00005	$0.00176

Measured 2mo ago against content hash 6d01af2df6af, method: parsed. Prices are Anthropic first-party input rates as of 2026-10-07, from the pricing page.

Security

Grade A, and why

css-nesting 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.

plugins/frontend/skills/css-nesting/SKILL.md · 171 lines

How it starts

The opening of the file, as written. The whole thing — 171 lines — stays where its author put it; the contents beside it link to each section on GitHub.

CSS Nesting with Stylelint Compliance

Flat-to-nested CSS conversion breaks when done incrementally because each edit shifts specificity ordering, triggering cascading linter errors. This skill prevents that by requiring upfront analysis before any edits.

When This Applies

Converting flat CSS selectors to nested & syntax
Fixing no-descending-specificity or no-duplicate-selectors errors after nesting
Any CSS restructuring that changes selector source order

The Two Rules You Must Satisfy

`no-descending-specificity`

Selectors matching the same DOM element must appear in ascending specificity order in source. A .foo (0,1,0) appearing after .bar:hover .foo (0,3,0) is an error because both can match a .foo element.

Selectors matching different elements don't conflict regardless of order.

`no-duplicate-selectors`

Two rule blocks resolving to the same selector are forbidden. Nesting changes resolved selectors: & .child inside .parent resolves to .parent .child. A second .parent block is a duplicate even if the contents differ.

Exception: the same selector inside vs outside a @media block is allowed (different parent nodes).

The Workflow

Step 1: Map the DOM hierarchy

Write out the parent-child nesting from the HTML template:

.container
  .wrapper
    .item
      .label

Step 2: List every selector with its specificity

For each selector in the flat CSS, calculate specificity and note which DOM element it matches:

.wrapper              (0,1,0)  matches .wrapper
.wrapper:hover        (0,2,0)  matches .wrapper
.item                 (0,1,0)  matches .item
.wrapper:hover .item  (0,3,0)  matches .item
.label                (0,1,0)  matches .label
.container:has(:hover) .wrapper:not(:has(:hover))  (0,4,0)  matches .wrapper

Step 3: Group by target element and sort ascending

For each element, the selectors that match it must appear in ascending specificity order in the final source:

Read the full file on GitHub · 171 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/honeycomb-plan.md 3.6 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 · 171 lines · 51 tokens per session scan A 6d01af2df6af

Subscribe to this mod's changes

css-nesting is a skill published in the GitHub repository fubits1/svelte-skills (10 stars, last pushed 12d ago), licensed MIT. It adds 51 tokens to every session and 1,760 once invoked, about $0.0002 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-nesting next to 6 skills from other repositories
Mod	Type	Stars	Last push	Licence	Scan	Tokens	Works with
css-nestingfubits1/svelte-skills	Skill	10	12d ago	MIT	A	51	Claude Code
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