A guide to making animations and visual effects with built-in CSS features, without adding a JavaScript animation library. CSS is the language that controls a website's appearance and layout.

Use it for scroll-based reveals, parallax, tooltips, popovers, page transitions, and elements that enter or leave the page.

It helps keep simple animations lightweight and avoids extra dependencies when modern browsers can handle the effect themselves.

How Jwuthri/Tracely-ai configures Claude Code and Codex

About the project

Tracely is a CI/CD system for AI agents that turns failed production traces into replayable regression tests. Development teams use it to detect and group agent failures, run the resulting cases on pull requests, and block changes that reproduce those failures. The catalogue entries provide skills for operating this trace-based testing and observability workflow.

Jwuthri/Tracely-ai · 1,311 stars · on GitHub · tracely-ai.com

Reuse

Borrowing it

Nothing to install: this file belongs to Jwuthri/Tracely-ai. Take a copy, put it at the same path in your own repository, and replace the rules that are about this project with yours.

Copy the file

curl -O https://raw.githubusercontent.com/Jwuthri/Tracely-ai/master/.agents/skills/css-native/SKILL.md

Clone the repo

git clone --depth 1 https://github.com/Jwuthri/Tracely-ai

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/jwuthri/tracely-ai/css-native/github.svg)](https://agentmods.dev/skills/jwuthri/tracely-ai/css-native)

Your own site

<a href="https://agentmods.dev/skills/jwuthri/tracely-ai/css-native"><img src="https://agentmods.dev/badge/skills/jwuthri/tracely-ai/css-native/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/jwuthri/tracely-ai/css-native"><img src="https://agentmods.dev/badge/skills/jwuthri/tracely-ai/css-native.svg" alt="Reviewed on agentmods" width="80" height="20"></a>

Per session 25 Skills are progressive disclosure: only the name and description are preloaded; the body loads when the skill is used.

When invoked 2,124 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. Third-party audits

NVIDIA SkillSpector pass 7 Sept 2026

How audits are shown

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	$0.00025	$0.02124
Opus 5.5	$0.00010	$0.00850
Sonnet 5.5	$0.00005	$0.00425
Haiku 4.5	$0.00003	$0.00212

Measured 2mo ago against content hash 28e2e1f065fe, method: parsed. Prices are Anthropic first-party input rates as of 2026-10-07, from the pricing page.

Security

Grade A, and why

css-native 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.

Origin

Copies of this mod

2 near-identical copies found in the catalogue:

css-native — 89% identical, 12 lines differ
css-native — 89% identical

.agents/skills/css-native/SKILL.md · 312 lines

How it starts

The opening of the file, as written. The whole thing — 312 lines — stays where its author put it; the contents beside it link to each section on GitHub.

CSS Native — Zero-Dependency Animations & Visual Techniques

When to Use CSS Native vs Library

Situation	Decision
< 3 animations on the page	CSS native
Scroll-driven reveal/parallax	CSS native (`animation-timeline`)
Enter/exit from `display: none`	CSS native (`@starting-style` + `transition-behavior: allow-discrete`)
Tooltip/popover positioning	CSS native (anchor positioning)
Page transitions (MPA or SPA)	CSS native (View Transitions API)
Complex multi-step timeline (5+ tweens)	GSAP
Stagger across dynamic list (unknown count)	GSAP or Framer Motion
Physics-based spring with interruption	Framer Motion
Morph between SVG shapes	GSAP MorphSVG

Rule of thumb: if you can express it in a @keyframes + one animation-timeline, stay in CSS. The moment you need imperative control, sequence coordination, or runtime values — reach for a library.

Scroll-Driven Animations

Scroll Progress Timeline

Animate based on scroll position of a container.

.progress-bar {
  animation: grow-width linear both;
  animation-timeline: scroll(root block);
}

@keyframes grow-width {
  from { transform: scaleX(0); }
  to   { transform: scaleX(1); }
}

scroll(<scroller> <axis>) — scroller: nearest | root | self, axis: block | inline | x | y
Default: scroll(nearest block)

View Progress Timeline

Animate as an element enters/exits the scrollport.

.reveal {
  animation: fade-in linear both;
  animation-timeline: view();
  animation-range: entry 0% entry 100%;
}

@keyframes fade-in {
  from { opacity: 0; transform: translateY(2rem); }
  to   { opacity: 1; transform: translateY(0); }
}

animation-range

Controls which segment of the timeline drives the animation.

/* Named ranges: cover | contain | entry | exit | entry-crossing | exit-crossing */
animation-range: entry 0% entry 100%;    /* animate during entry only */
animation-range: contain 0% contain 100%; /* animate while fully visible */
animation-range: entry 25% exit 75%;      /* custom start/end */

Read the full file on GitHub · 312 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/modern-css.md 11 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 · 312 lines · 25 tokens per session scan A 28e2e1f065fe

Subscribe to this mod's changes

css-native is a skill published in the GitHub repository Jwuthri/Tracely-ai (1,311 stars, last pushed yesterday), licensed MIT. It adds 25 tokens to every session and 2,124 once invoked, about $0.0001 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 2026-08-30.

CI and CD Creative and media Frontend ai-agents evals llm-evaluation llm-observability llm-ops

css-native next to 6 skills from other repositories
Mod	Type	Stars	Last push	Licence	Scan	Tokens	Works with
css-nativeJwuthri/Tracely-ai	Skill	1.3k	yesterday	MIT	A	25	Claude Code, Codex
factory-releasetikalk/adlc-team-skills	Skill	145	yesterday	MIT	A	72	Claude Code, Codex
pin-mcp-serversyotambraun/Toolscore	Skill	6	6d ago	Apache-2.0	A	107	Claude Code
Prompt Version Control WorkflowNotysoty/openagentskills	Skill	9	2mo ago	MIT	A	30	Claude Code, Codex
llm-testerbuiphucminhtam/forgewright	Skill	49	2d ago	none	A	49	Claude Code
report-repairastandrik/my_instructions	Skill	6	1mo ago	MIT	A	16	Claude Code
local-validatorastandrik/my_instructions	Skill	6	1mo ago	MIT	A	20	Claude Code

Tracely-ai: Skill for Claude Code