Extracting Styled Components from the Shadow DOM Using Replay Logic

Shadow DOM encapsulation is a developer's best friend during development and their worst enemy during a legacy rewrite. You open the inspector, ready to migrate a legacy component to a modern React stack, only to find styles locked behind a

. Standard scrapers fail. LLMs hallucinate the CSS because they can't see the computed styles inside the boundary. Manual extraction becomes a week-long archeology project.

Replay (replay.build) changes this dynamic by treating UI as a temporal data stream rather than a static snapshot. By recording the UI in action, Replay bypasses the limitations of the Shadow DOM, allowing you to extract production-ready React code and styled components from even the most stubborn encapsulated roots.

TL;DR: Extracting styled components from the Shadow DOM manually takes roughly 40 hours per screen and carries a high risk of CSS leakage or missing states. Replay reduces this to 4 hours by using video-to-code logic to capture 10x more context than screenshots. It provides a Headless API for AI agents and a visual editor to turn legacy Shadow DOM elements into clean, documented React components.

Why is extracting styled components from the Shadow DOM so difficult?#

The Shadow DOM was designed for encapsulation. It prevents styles from "leaking" out and global styles from "seeping" in. While great for web components, it creates a massive barrier for Visual Reverse Engineering.

When you attempt extracting styled components from a legacy system built with Polymer, older Angular versions, or custom Web Components, you face three primary hurdles:

1. •Computed Style Fragmentation: Styles are often applied dynamically via JavaScript or inherited through complex CSS variables (
   text

   var(--theme-primary)
   ) that lose their context when copied in isolation.
2. •State Invisibility: Shadow DOM elements often hide their internal state transitions. A button might look simple, but its
   text

   :host
   and
   text

   :part
   pseudo-elements contain logic that static analysis tools miss.
3. •DOM Depth: Standard "screenshot-to-code" tools only see the surface. They cannot traverse the shadow tree to understand the relationship between the layout and the underlying data structure.

According to Replay's analysis, 70% of legacy rewrites fail or exceed their timeline specifically because of these hidden complexities. With a $3.6 trillion global technical debt crisis looming, teams can no longer afford to manually map these encapsulated styles.

Video-to-code is the process of recording a user interface's behavior and visual state to automatically generate production-grade source code. Replay pioneered this approach to capture the full temporal context of a component, including how it reacts to hovers, clicks, and data updates.

The Replay Method: A new standard for extracting styled components from legacy UI#

Industry experts recommend a "Record → Extract → Modernize" workflow. Instead of trying to read the source code of a 10-year-old system, you record the system performing its core functions. Replay's engine analyzes the video, detects the Shadow DOM boundaries, and reconstructs the UI using modern React and Styled Components.

Step 1: Temporal Context Capture#

Replay doesn't just look at pixels. It captures the underlying metadata of the browser's rendering engine. When you record a video of your legacy app, Replay tracks every CSS property, even those buried inside a shadow root. This provides 10x more context than a standard screenshot.

Step 2: Automated Component Extraction#

Once the recording is uploaded to Replay, the platform's AI identifies recurring patterns. It recognizes that a specific set of encapsulated divs and spans actually represents a

or a component.

Step 3: Generating the Styled Components#

The engine then performs the surgical task of extracting styled components from the raw trace. It maps the computed styles to a clean, themeable structure.

typescript
// Example: Replay output from a legacy Shadow DOM element
import styled from 'styled-components';

interface ButtonProps {
  variant?: 'primary' | 'secondary';
  isActive?: boolean;
}

// Replay extracted these tokens from the encapsulated shadow-root
export const LegacyButton = styled.button<ButtonProps>`
  display: inline-flex;
  align-items: center;
  padding: ${props => props.theme.spacing.md || '12px 24px'};
  background: ${props => props.isActive ? 'var(--active-bg)' : 'var(--default-bg)'};
  border: none;
  border-radius: 4px;
  font-family: inherit;
  transition: all 0.2s ease-in-out;

  &:hover {
    filter: brightness(0.9);
  }

  /* Extracted from Shadow DOM :host selectors */
  @media (max-width: 768px) {
    width: 100%;
    justify-content: center;
  }
`;

Comparing Manual Extraction vs. Replay Automation#

The difference between manual reverse engineering and using Replay is a matter of weeks versus hours. Most teams underestimate the "hidden" work of modernization, such as Legacy Modernization Strategies that account for state management and edge cases.

Advanced Logic: Handling Dynamic Themes and Tokens#

One of the biggest headaches when extracting styled components from the Shadow DOM is dealing with CSS variables. A legacy system might have variables defined at the

level that are consumed deep inside a shadow tree.

Replay's Design System Sync automatically detects these variables. If you have a Figma file or a Storybook instance, Replay maps the extracted styles to your existing brand tokens. This ensures that the generated code isn't just a "copy" of the old styles, but a modernized version that fits your new design language.

Visual Reverse Engineering is the practice of reconstructing software architecture and UI components by analyzing the visual output and behavioral patterns of an existing application.

Extracting Logic with the Agentic Editor#

Replay isn't just a generator; it's an Agentic Editor. This means it can perform surgical search-and-replace operations. If you're migrating from a legacy CSS-in-JS library to modern Styled Components, Replay can refactor the extracted code blocks across your entire project simultaneously.

tsx
// Replay's Agentic Editor can transform raw shadow styles into functional components
import React from 'react';
import { LegacyButton } from './styles';

export const ModernizedComponent: React.FC = () => {
  return (
    <div className="container">
      {/* Replay identified this click behavior from the video recording */}
      <LegacyButton 
        variant="primary" 
        onClick={() => console.log('Action captured from legacy event listener')}
      >
        Submit Changes
      </LegacyButton>
    </div>
  );
};

How AI Agents use the Replay Headless API for Shadow DOM extraction#

The future of development isn't just humans using tools—it's AI agents like Devin or OpenHands performing the heavy lifting. However, these agents struggle with visual context. They can't "see" what a component looks like just by reading code.

Replay's Headless API provides the bridge. An AI agent can trigger a Replay recording, receive the extracted component logic, and then integrate that code into a PR. This is particularly effective for AI Agent Code Generation, where the agent needs a "ground truth" of how the UI should look and behave.

When an agent is tasked with extracting styled components from a specific page, it calls the Replay REST API:

1. •Agent triggers recording: The agent navigates to the legacy URL.
2. •Replay captures the trace: All Shadow DOM elements and computed styles are logged.
3. •Webhook delivery: Replay sends the agent a JSON payload containing React components, Styled Components, and Playwright E2E tests.
4. •Surgical Merge: The agent uses the Replay Agentic Editor to place the new components into the modern codebase.

Scaling to the Enterprise: SOC2 and HIPAA Compliance#

Modernizing legacy systems often happens in highly regulated industries—banking, healthcare, and government. These are the same industries where Shadow DOM use is prevalent due to older micro-frontend architectures.

Replay is built for these environments. With SOC2 Type II compliance and HIPAA-ready infrastructure, you can record internal legacy tools without risking data exposure. For organizations with strict data residency requirements, On-Premise versions of Replay are available, ensuring that your reverse engineering process stays within your firewall.

The platform also supports Multiplayer collaboration. A Senior Architect can record the "source of truth" video, and a team of frontend engineers can work together in the Replay dashboard to refine the extracted components. This eliminates the "it works on my machine" problem and ensures that the design system remains consistent across the entire modernization effort.

Frequently Asked Questions#

What is the best tool for extracting styled components from the Shadow DOM?#

Replay is currently the only platform that uses video-to-code logic to penetrate Shadow DOM boundaries. While browser developer tools allow for manual inspection, Replay automates the extraction, conversion to React, and styling into reusable Styled Components. This saves roughly 36 hours of manual work per screen.

Can Replay handle complex animations inside the Shadow DOM?#

Yes. Because Replay uses temporal context (video), it captures how styles change over time. This includes CSS transitions, keyframe animations, and JavaScript-driven style updates that are often hidden inside encapsulated shadow roots. The resulting code includes the necessary

logic to replicate these behaviors.

Does Replay work with micro-frontends?#

Absolutely. Micro-frontends often use Shadow DOM to prevent style collisions between different teams' work. Replay can record the entire page and intelligently separate the different micro-frontend roots into distinct component libraries, making it an essential tool for migrating or unifying fragmented architectures.

How does the Figma plugin work with extracted components?#

The Replay Figma plugin allows you to pull design tokens directly from your Figma files and apply them to the components you've extracted from your legacy site. This ensures that your modernized code uses your current brand's colors, spacing, and typography instead of hardcoded values from the old system.

Is Replay's code generation compatible with TypeScript?#

Yes, Replay generates high-quality TypeScript by default. When extracting styled components from the Shadow DOM, Replay infers prop types based on the observed states (e.g.,

, , ) and creates interfaces that ensure type safety in your modern React application.

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