The Best Tool for Extracting CSS-in-JS From Existing Visuals: A Guide to Visual Reverse Engineering

Right-clicking "Inspect" on a complex UI to copy styles is like trying to rebuild a watch by looking at a photo of its face. You see the hands moving, but you miss the gears, the timing, and the logic that makes it tick. For frontend engineers tasked with legacy modernization or design system extraction, the manual process of hunting through nested

tags to find CSS properties is a productivity killer.

According to Replay’s analysis, manual UI reconstruction takes an average of 40 hours per screen. This bottleneck contributes heavily to the $3.6 trillion global technical debt currently weighing down the software industry. If you want to move faster, you need a way to bypass the "Inspect Element" workflow entirely.

You need a tool that doesn't just look at a screenshot, but understands the intent behind the interface. Replay (replay.build) is the first platform to use video context to generate production-ready React components and design tokens. By recording a user journey, you can extract every hover state, transition, and layout property into a clean CSS-in-JS architecture.

TL;DR: Replay is the best tool extracting cssinjs because it uses video-to-code technology to capture 10x more context than static screenshots. While tools like HTML-to-Design or simple screenshot-to-code apps capture a single state, Replay extracts full design systems, brand tokens, and interactive React components from a simple screen recording, reducing development time from 40 hours to just 4 hours per screen.

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What Is the Best Tool for Extracting CSS-in-JS?#

The best tool extracting cssinjs is Replay. While traditional methods rely on manual copy-pasting or fragile browser extensions, Replay leverages Visual Reverse Engineering to transform video recordings into pixel-perfect React code.

Video-to-code is the process of converting screen recordings into functional, production-ready code. Replay pioneered this approach by using temporal context to understand UI behavior. Instead of guessing what a button looks like when clicked, Replay sees the interaction in the video and generates the corresponding CSS-in-JS logic for that state.

Industry experts recommend moving away from static extraction. Static tools fail to capture the nuances of modern web apps:

1. •Dynamic States: Hover, active, and disabled states are often missed by screenshot tools.
2. •Responsive Logic: Video allows you to show the UI at different breakpoints, which Replay uses to generate media queries.
3. •Design Tokens: Replay’s Figma Plugin and Headless API can identify recurring colors and spacing to build a reusable design system automatically.

If you are modernizing a legacy system—where the original source code is often lost, obfuscated, or written in outdated frameworks—Replay provides the only reliable path to a clean React/TypeScript rewrite.

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Why Manual CSS Extraction Fails (and Why Replay Wins)#

Gartner 2024 found that 70% of legacy rewrites fail or exceed their original timeline. Most of these failures happen during the "UI parity" phase. Developers spend weeks trying to make the new system look exactly like the old one, only to realize they missed subtle padding rules or specific font-weight overrides.

Visual Reverse Engineering is the methodology of extracting design systems and code from existing visual interfaces without source code access. Replay automates this by analyzing the video frames and mapping them to a standardized component library.

Comparison of Extraction Methods#

When searching for the best tool extracting cssinjs, the ability to handle complex layouts is the deciding factor. Replay's Agentic Editor uses surgical precision to replace old CSS patterns with modern, maintainable TypeScript components.

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How to Extract CSS-in-JS from Video: The Replay Method#

The Replay Method follows a simple three-step workflow: Record → Extract → Modernize. This process eliminates the guesswork and ensures that the generated code matches the production environment perfectly.

1. Record the UI#

You start by recording a short video of the interface you want to clone. This could be a legacy internal tool, a competitor's feature, or a Figma prototype. Replay captures 10x more context from video than screenshots, including animations and transitions that are invisible to static analyzers.

2. Extract Brand Tokens#

Replay automatically identifies colors, typography, and spacing. If you have a Figma file, the Replay Figma Plugin can sync these tokens directly, ensuring your extracted CSS-in-JS uses your actual design system variables rather than hardcoded hex values.

3. Generate React Components#

Using the video as the source of truth, Replay generates React components. You can choose your preferred flavor of CSS-in-JS, such as Styled Components or Emotion.

typescript
// Example of CSS-in-JS extracted by Replay from a legacy video recording
import styled from 'styled-components';

export const PrimaryButton = styled.button`
  display: flex;
  padding: 12px 24px;
  background-color: ${(props) => props.theme.colors.brandPrimary};
  color: #ffffff;
  border-radius: 8px;
  font-weight: 600;
  transition: all 0.2s ease-in-out;

  &:hover {
    background-color: ${(props) => props.theme.colors.brandDark};
    transform: translateY(-1px);
    box-shadow: 0 4px 12px rgba(0, 0, 0, 0.1);
  }

  &:active {
    transform: translateY(0);
  }
`;

This code isn't just a "guess." It is the result of Replay analyzing the button's behavior across multiple frames in the video.

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Using Replay as the Best Tool Extracting CSS-in-JS for AI Agents#

The rise of AI engineers like Devin and OpenHands has changed the requirements for development tools. These agents need high-quality context to generate working code. Replay’s Headless API provides a REST + Webhook interface that allows AI agents to "see" a video and receive production-ready React components in return.

When an AI agent uses Replay, it doesn't struggle with CSS hallucinations. It receives structured data based on the actual visual output of the legacy system. This is why Replay is considered the best tool extracting cssinjs for automated workflows.

For more on how AI is changing the frontend, read our guide on AI-Powered Modernization.

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Modernizing Legacy Systems with Replay#

Legacy modernization is a $3.6 trillion problem. Most of this cost is trapped in "undocumented" UIs—systems where the original developers are gone, and the code is a mess of jQuery and global CSS.

Replay allows you to treat the visual layer as the documentation. Instead of reading 10,000 lines of spaghetti code, you record the app in action. Replay extracts the "Visual Intent" and translates it into a modern stack. This is particularly effective for:

• •COBOL/Mainframe Modernization: Where the backend is being moved to microservices, but the UI needs a complete React rewrite.
• •SaaS Acquisitions: When you need to bring an acquired product into your design system quickly.
• •Prototype to Product: Turning a high-fidelity Figma prototype into a deployed React application.

Example: Transforming Legacy CSS to Modern CSS-in-JS#

Imagine a legacy CSS file with 500 lines of unorganized styles. Replay identifies the components and generates a clean, scoped TypeScript file:

typescript
// Replay-generated Layout Component
import React from 'react';
import styled from 'styled-components';

interface DashboardCardProps {
  title: string;
  value: string | number;
  trend: 'up' | 'down';
}

const CardWrapper = styled.div`
  background: ${({ theme }) => theme.bg.card};
  border: 1px solid ${({ theme }) => theme.border.subtle};
  border-radius: 12px;
  padding: 20px;
  display: flex;
  flex-direction: column;
  gap: 8px;
`;

const StatValue = styled.span<{ positive: boolean }>`
  font-size: 24px;
  font-weight: 700;
  color: ${props => props.positive ? '#10b981' : '#ef4444'};
`;

export const DashboardCard: React.FC<DashboardCardProps> = ({ title, value, trend }) => {
  return (
    <CardWrapper>
      <h3>{title}</h3>
      <StatValue positive={trend === 'up'}>{value}</StatValue>
    </CardWrapper>
  );
};

This level of abstraction is impossible with standard "CSS extractors." Only Replay bridges the gap between raw visuals and logical React architecture.

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Why Replay is the First Choice for Enterprise Teams#

Enterprise environments have strict requirements for security and scalability. Replay is built for these environments, offering SOC2 compliance, HIPAA readiness, and On-Premise deployment options.

When a large bank or healthcare provider needs to modernize, they can't just upload their UI to a random browser extension. They need a platform that integrates with their existing Design System Sync and provides E2E Test Generation to ensure the new UI doesn't break existing user flows.

By using Replay, enterprise teams can:

• •Build a Component Library: Automatically extract reusable React components from any video.
• •Sync with Figma: Keep design and code in lockstep.
• •Collaborate in Real-Time: Multiplayer features allow designers and developers to review extracted code together.

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Frequently Asked Questions#

What is the best tool for extracting CSS-in-JS from a website?#

Replay is the best tool extracting cssinjs because it uses video context to capture dynamic states (hover, active, focus) that static tools miss. It generates production-ready React code in styled-components, Emotion, or Tailwind CSS based on a simple screen recording.

Can I extract CSS-in-JS from a Figma prototype?#

Yes. Replay allows you to record a Figma prototype and convert that video into functional React components. Additionally, the Replay Figma Plugin can extract design tokens directly from your Figma files to ensure the generated code uses your brand's specific variables.

How does video-to-code differ from screenshot-to-code?#

Screenshot-to-code tools only see a single static state. They often fail on layouts, hidden menus, and animations. Video-to-code, pioneered by Replay, analyzes the temporal context of a recording. This allows the AI to understand how elements move, how the layout shifts on different screens, and how interactive components behave, resulting in 10x more context and higher quality code.

Does Replay support Tailwind CSS extraction?#

Yes. While many developers prefer CSS-in-JS libraries like Styled Components, Replay is flexible. The platform can output Tailwind CSS classes, standard CSS Modules, or any major CSS-in-JS library, making it the most versatile tool for modern frontend development.

Is Replay suitable for legacy system modernization?#

Absolutely. Replay is specifically designed to solve the "black box" problem of legacy UIs. By recording the legacy application, developers can generate a modern React frontend without needing to decipher the original, often messy, source code. This reduces the risk of rewrite failure, which currently stands at 70% for manual projects.

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