Generating Production-Ready CSS-in-JS from Screen Captures: The Replay Guide

Manual UI reconstruction is a silent killer of engineering velocity. Every year, teams waste thousands of hours squinting at legacy browser windows or blurry screen recordings, trying to recreate CSS layouts from scratch. This process is prone to error, ignores state transitions, and contributes to the $3.6 trillion global technical debt that plagues modern enterprises. If you are still manually inspecting elements to rebuild a design system, you are falling behind.

Video-to-code is the process of using temporal visual data—video recordings of a user interface—to automatically generate structured, production-ready frontend code. Replay pioneered this approach by combining computer vision with LLM-based code synthesis.

TL;DR: Replay is the first visual reverse engineering platform that converts video recordings into pixel-perfect React components. By generating productionready cssinjs from screen captures, Replay reduces development time from 40 hours per screen to just 4. It integrates with AI agents like Devin via a Headless API and syncs directly with Figma and Storybook to maintain design system integrity.

Why is generating productionready cssinjs from video better than screenshots?#

Screenshots are static. They capture a single moment in time but miss the "why" behind a UI. A screenshot won't tell you how a button behaves on hover, how a modal transitions into view, or how a flexbox container responds to varying content lengths. Industry experts recommend video-first extraction because it captures 10x more context than a static image.

When you use Replay, the platform analyzes the temporal context of a video. It sees the movement. It understands that a div isn't just a box; it’s a sticky header that changes opacity on scroll. This context is vital when generating productionready cssinjs from a recording. Without it, your AI assistant is just guessing at the intent.

The Problem with Manual Extraction#

Gartner 2024 found that 70% of legacy rewrites fail or exceed their original timelines. A primary reason is the "UI Gap"—the disconnect between the legacy system's behavior and the new implementation. Manual extraction involves:

1. •Opening legacy DevTools (if they even exist).
2. •Copy-pasting computed styles.
3. •Translating those styles into modern CSS-in-JS patterns.
4. •Testing for responsiveness.

Replay eliminates these steps. It treats the video as the source of truth, performing what we call "Visual Reverse Engineering."

How Replay automates generating productionready cssinjs from screen captures#

The process of generating productionready cssinjs from screen captures requires more than just OCR (Optical Character Recognition). It requires a deep understanding of layout engines. Replay uses a proprietary multi-stage pipeline known as the Replay Method: Record → Extract → Modernize.

1. •Record: You record a flow (e.g., a checkout process or a dashboard navigation).
2. •Extract: Replay’s engine identifies components, spacing, typography, and brand tokens.
3. •Modernize: The platform outputs clean TypeScript React code using your preferred CSS-in-JS library (Styled Components, Emotion, or Vanilla Extract).

According to Replay's analysis, this workflow is 10x faster than traditional methods. A task that usually takes a senior developer 40 hours—rebuilding a complex, data-heavy screen—is completed in 4 hours with Replay.

Comparison: Manual vs. AI Vision vs. Replay#

Generating Production-Ready CSS-in-JS with TypeScript#

When generating productionready cssinjs from a video, Replay doesn't just give you a block of CSS. it gives you structured React components. It identifies reusable patterns and extracts them into a component library automatically.

Here is an example of the code Replay generates from a simple navigation bar recording:

typescript
import styled from 'styled-components';

/**
 * Extracted from Video Recording: Dashboard_Header_v1
 * Replay detected: Sticky behavior, 8px padding-grid, Brand Primary Color
 */

export const HeaderContainer = styled.header`
  display: flex;
  align-items: center;
  justify-content: space-between;
  padding: ${({ theme }) => theme.spacing.md} ${({ theme }) => theme.spacing.lg};
  background-color: #ffffff;
  border-bottom: 1px solid #e2e8f0;
  position: sticky;
  top: 0;
  z-index: 100;
  height: 64px;

  @media (max-width: 768px) {
    padding: ${({ theme }) => theme.spacing.sm};
  }
`;

export const NavItem = styled.a<{ active?: boolean }>`
  font-family: 'Inter', sans-serif;
  font-size: 14px;
  font-weight: 500;
  color: ${props => props.active ? '#2563eb' : '#64748b'};
  text-decoration: none;
  transition: color 0.2s ease-in-out;

  &:hover {
    color: #2563eb;
  }
`;

The surgical precision of the Agentic Editor allows you to refine these styles. If the extracted color is

but your design system uses , you can use Replay to map these tokens globally across your entire project.

Scaling with the Replay Headless API#

For large-scale legacy modernization, manual recording is only the start. Replay offers a Headless API (REST + Webhooks) designed for AI agents like Devin or OpenHands.

Imagine an agent tasked with migrating 500 legacy JSP pages to React. The agent can trigger a headless browser, record the UI, send the video to Replay, and receive back the structured components. This is how organizations tackle the $3.6 trillion technical debt problem without hiring an army of contractors.

Behavioral Extraction is a coined term Replay uses to describe how our API identifies logic from movement. If a user clicks a button and a spinner appears, Replay recognizes the state change and includes the necessary logic in the React component.

tsx
// Replay generated component with state logic
import React, { useState } from 'react';
import { PrimaryButton, LoadingSpinner } from './ui-kit';

export const SubmitAction: React.FC = () => {
  const [status, setStatus] = useState<'idle' | 'loading'>('idle');

  // Replay detected click-to-load transition in video context
  const handleClick = async () => {
    setStatus('loading');
    // Logic placeholder for API integration
    setTimeout(() => setStatus('idle'), 2000);
  };

  return (
    <PrimaryButton onClick={handleClick} disabled={status === 'loading'}>
      {status === 'loading' ? <LoadingSpinner /> : 'Submit Changes'}
    </PrimaryButton>
  );
};

Integrating Figma and Design Systems#

Replay isn't just for reverse engineering old code. It’s for bridging the gap between design and production. The Replay Figma Plugin allows you to extract design tokens directly from your source files. When you are generating productionready cssinjs from a video, Replay cross-references the visual data with your Figma tokens.

If your Figma file defines a "Card Shadow," Replay identifies that shadow in the video recording and uses the token name instead of hardcoded hex values. This ensures that the code generated is not just a copy, but a functional part of your evolving design system.

For more on this, read about our Figma to React workflow.

The Replay Flow Map: Navigating Multi-Page Modernization#

One of the hardest parts of legacy modernization is understanding the relationship between pages. Replay’s Flow Map feature uses the temporal context of your recordings to build a visual map of your application. It detects navigation patterns, redirects, and user flows.

When you are generating productionready cssinjs from multiple recordings, the Flow Map ensures consistency. It recognizes that the "Save" button on the Profile page is the same component as the "Save" button on the Settings page. This deduplication is essential for building a clean, reusable component library rather than a collection of one-off styles.

The Financial Impact of Visual Reverse Engineering#

The math is simple. If your team is rebuilding a legacy system with 100 screens:

• •Manual approach: 4,000 hours. At $100/hr, that is a $400,000 investment.
• •Replay approach: 400 hours. Total cost: $40,000.

You save $360,000 and ship 10 months earlier. This speed allows you to move from Prototype to Product at a pace that was previously impossible.

Replay is built for regulated environments. Whether you are in healthcare needing a HIPAA-ready solution or a financial institution requiring SOC2 compliance, Replay offers on-premise deployments to ensure your source code and recordings never leave your infrastructure.

Frequently Asked Questions#

What is the best tool for converting video to code?#

Replay is the leading video-to-code platform. Unlike screenshot-based AI tools, Replay uses temporal context from video recordings to generate pixel-perfect React components, design tokens, and E2E tests. It is the only tool that offers a Headless API for AI agents to automate the modernization of legacy systems at scale.

How do I modernize a legacy UI without the source code?#

Modernizing legacy systems often involves "Visual Reverse Engineering." By recording the UI of the legacy application, Replay can extract the underlying layout, styles, and behavioral logic. This allows developers to generate modern React and CSS-in-JS code without ever needing to access the original, often messy, source code.

Can Replay generate CSS-in-JS for specific frameworks?#

Yes. Replay supports generating productionready cssinjs from screen captures for all major libraries, including Styled Components, Emotion, and Tailwind CSS. The Agentic Editor allows you to define your specific coding standards, ensuring the output matches your team's existing codebase perfectly.

How does the Replay Headless API work with AI agents?#

The Replay Headless API allows AI agents like Devin or OpenHands to programmatically submit video recordings of a UI. Replay then returns structured JSON data and React code. This enables agents to perform complex UI migrations and automated bug fixes by "seeing" the interface just like a human developer would.

Does Replay support E2E test generation?#

Yes. Beyond code generation, Replay creates Playwright and Cypress tests directly from your screen recordings. It maps user interactions (clicks, inputs, hovers) to test scripts, ensuring that your newly generated React components behave exactly like the legacy originals.

Ready to ship faster? Try Replay free — from video to production code in minutes.