pseudo-elements

Q: How do I install pseudo-elements?

Run npx skills add https://github.com/raphaelsalaja/userinterface-wiki --skill pseudo-elements in your project. The skills CLI detects the agents you use and copies the skill into the right folder. For Claude Code you can also place the skill folder at ~/.claude/skills/pseudo-elements/ (personal) or .claude/skills/pseudo-elements/ (project).

by raphaelsalajaFrontend & Design

Audit CSS for pseudo-element best practices and View Transitions API usage. Use when reviewing hover effects, decorative layers, or page transitions. Outputs file:line findings.

Installs: 139
Last 24h: —
Trending rank: —
Security: Not audited

Install

Works with every agent the skills CLI supports.

npx skills add https://github.com/raphaelsalaja/userinterface-wiki --skill pseudo-elements

01
Install
Run the command in your project. The CLI asks which agents to install for.
02
Describe the task
Ask your agent for something this skill covers. It loads pseudo-elements automatically when relevant.
03
Review the result
The agent follows the SKILL.md steps, scripts and references bundled with the skill.

SKILL.md

The instructions your agent reads when the skill is triggered.

Pseudo Elements

Review CSS and JavaScript for pseudo-element best practices and View Transitions API usage.

How It Works

Read the specified files (or prompt user for files/pattern)
Check against all rules below
Output findings in file:line format

Rule Categories

Priority	Category	Prefix
1	Before/After	`pseudo-`
2	View Transitions	`transition-`
3	Native Styling	`native-`

Rules

Before/After Rules

`pseudo-content-required`

::before and ::after require content property to render.

Fail:

.button::before {
  position: absolute;
  background: var(--gray-3);
}

Pass:

.button::before {
  content: "";
  position: absolute;
  background: var(--gray-3);
}

`pseudo-over-dom-node`

Use pseudo-elements for decorative content instead of extra DOM nodes.

Fail:

<button className={styles.button}>
  <span className={styles.background} /> {/* Unnecessary DOM node */}
  Click me
</button>

Pass:

<button className={styles.button}>
  Click me
</button>

.button::before {
  content: "";
  /* decorative background */
}

`pseudo-position-relative-parent`

Parent must have position: relative for absolute pseudo-elements.

Fail:

.button::before {
  content: "";
  position: absolute;
  inset: 0;
}
/* .button has no position */

Pass:

.button {
  position: relative;
}

.button::before {
  content: "";
  position: absolute;
  inset: 0;
}

`pseudo-z-index-layering`

Pseudo-elements need z-index to layer correctly with content.

Fail:

.button::before {
  content: "";
  position: absolute;
  inset: 0;
  background: var(--gray-3);
}
/* Covers button text */

Pass:

.button {
  position: relative;
  z-index: 1;
}

.button::before {
  content: "";
  position: absolute;
  inset: 0;
  background: var(--gray-3);
  z-index: -1;
}

`pseudo-hit-target-expansion`

Use negative inset values to expand hit targets without extra markup.

Fail:

<div className={styles.wrapper}> {/* Extra wrapper for hit target */}
  <a className={styles.link}>Link</a>
</div>

Pass:

.link {
  position: relative;
}

.link::before {
  content: "";
  position: absolute;
  inset: -8px -12px;
}

View Transitions Rules

`transition-name-required`

Elements participating in view transitions need view-transition-name.

Fail:

document.startViewTransition(() => {
  // No view-transition-name assigned
  targetImg.src = newSrc;
});

Pass:

sourceImg.style.viewTransitionName = "card";
document.startViewTransition(() => {
  sourceImg.style.viewTransitionName = "";
  targetImg.style.viewTransitionName = "card";
});

`transition-name-unique`

Each view-transition-name must be unique on the page during transition.

Fail:

.card {
  view-transition-name: card;
}
/* Multiple cards with same name */

Pass:

// Assign unique name only to transitioning element
element.style.viewTransitionName = `card-${id}`;

`transition-name-cleanup`

Remove view-transition-name after transition completes.

Fail:

sourceImg.style.viewTransitionName = "card";
document.startViewTransition(() => {
  targetImg.style.viewTransitionName = "card";
});
// sourceImg still has name, causes conflict on next transition

Pass:

sourceImg.style.viewTransitionName = "card";
document.startViewTransition(() => {
  sourceImg.style.viewTransitionName = "";
  targetImg.style.viewTransitionName = "card";
});

`transition-over-js-library`

Prefer View Transitions API over JavaScript animation libraries for page transitions.

Fail:

import { motion } from "motion/react";

function ImageLightbox() {
  return (
    <motion.img layoutId="hero" /> // JS-based shared element transition
  );
}

Pass:

function openLightbox(img: HTMLImageElement) {
  img.style.viewTransitionName = "hero";
  document.startViewTransition(() => {
    // Native browser transition
  });
}

`transition-style-pseudo-elements`

Style view transition pseudo-elements for custom animations.

Fail:

document.startViewTransition(() => { /* ... */ });
// Uses default crossfade

Pass:

::view-transition-group(card) {
  animation-duration: 300ms;
  animation-timing-function: cubic-bezier(0.215, 0.61, 0.355, 1);
}

Native Styling Rules

`native-backdrop-styling`

Use ::backdrop pseudo-element for dialog/popover backgrounds.

Fail:

<>
  <div className={styles.overlay} onClick={close} />
  <dialog className={styles.dialog}>{children}</dialog>
</>

Pass:

dialog::backdrop {
  background: var(--black-a6);
  backdrop-filter: blur(4px);
}

`native-placeholder-styling`

Use ::placeholder for input placeholder styling, not wrapper elements.

Fail:

<div className={styles.inputWrapper}>
  {!value && <span className={styles.placeholder}>Enter text...</span>}
  <input value={value} />
</div>

Pass:

input::placeholder {
  color: var(--gray-9);
  opacity: 1;
}

`native-selection-styling`

Use ::selection for text selection styling.

Pass:

::selection {
  background: var(--blue-a5);
  color: var(--gray-12);
}

Output Format

When reviewing files, output findings as:

file:line - [rule-id] description of issue

Example:
components/button/styles.module.css:12 - [pseudo-content-required] ::before missing content property
components/lightbox/index.tsx:45 - [transition-over-js-library] Using motion layoutId instead of View Transitions API

Summary Table

After findings, output a summary:

Rule	Count	Severity
`pseudo-content-required`	2	HIGH
`pseudo-over-dom-node`	1	MEDIUM
`transition-name-cleanup`	1	MEDIUM

References

FAQ

What does the pseudo-elements skill do?

Audit CSS for pseudo-element best practices and View Transitions API usage. Use when reviewing hover effects, decorative layers, or page transitions. Outputs file:line findings.

How do I install pseudo-elements?

Run npx skills add https://github.com/raphaelsalaja/userinterface-wiki --skill pseudo-elements in your project. The skills CLI detects the agents you use and copies the skill into the right folder. For Claude Code you can also place the skill folder at ~/.claude/skills/pseudo-elements/ (personal) or .claude/skills/pseudo-elements/ (project).

Which AI agents can use pseudo-elements?

Any agent that supports the open Agent Skills format (a folder with a SKILL.md file), including Claude Code, Codex, Cursor, GitHub Copilot, Gemini CLI, Windsurf, Cline, OpenCode and more.

Is pseudo-elements safe to install?

No partner security audit is available yet. Skills can run commands and scripts, so read the SKILL.md and any bundled files before installing.

Who maintains pseudo-elements?

It is published by raphaelsalaja in raphaelsalaja/userinterface-wiki. It has 139 recorded installs.