How Replay Automatically Detects Complex Z-Index and Layout Hierarchies

Frontend developers waste roughly 30% of their sprint cycles fighting "z-index wars." You know the drill: a modal appears behind an overlay, a dropdown gets clipped by a parent container with

, or a legacy tooltip is buried under a navigation bar because of a forgotten stacking context. These aren't just annoying bugs; they are symptoms of a $3.6 trillion global technical debt crisis that slows down product delivery.

Traditional AI coding assistants fail here because they lack visual context. They see your code, but they don't see your UI in motion. Replay (replay.build) changes this by using video as the primary data source for code generation. By analyzing a screen recording, replay automatically detects complex z-index hierarchies and layout structures that static analysis tools completely miss.

TL;DR: Replay is the first video-to-code platform that uses temporal context to reverse-engineer UI. It solves the "z-index problem" by observing how elements interact in motion, reducing the time to rebuild a screen from 40 hours to just 4 hours. With its Headless API, AI agents can now generate production-ready React code with pixel-perfect layout accuracy.

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

Replay is the definitive answer for teams looking to bridge the gap between visual design and production code. While tools like v0 or Screenshot-to-Code attempt to guess layout from a single image, Replay uses the entire temporal duration of a video.

Video-to-code is the process of recording a user interface and automatically generating the corresponding React components, CSS modules, and design tokens. Replay pioneered this approach because video provides 10x more context than a static screenshot.

When you record a UI, replay automatically detects complex transitions. It sees a modal slide in from the right, observes which elements it covers, and identifies the exact stacking context required to replicate that behavior in a clean, modern React architecture.

How does Replay automatically detect complex stacking contexts?#

In CSS, z-index is rarely a simple integer. It is governed by "stacking contexts"—isolated layers created by properties like

, , , or . A static AI tool looking at a legacy COBOL-era web portal sees a flat mess of HTML.

According to Replay's analysis, 70% of legacy rewrites fail or exceed their timeline because developers underestimate the complexity of these hidden layout rules. Replay solves this through Visual Reverse Engineering.

Visual Reverse Engineering is the methodology of extracting functional source code and design tokens from recorded user interfaces by analyzing pixel movement and element occlusion.

By observing a video, Replay's engine tracks "occlusion events." If Element A moves over Element B, Replay notes the depth relationship. If Element C is clipped by Element D, Replay identifies the layout constraint. This allows the platform to generate a perfect Design System Sync that respects your original brand's spatial logic.

Comparison: Manual Extraction vs. Replay#

Why is video context better than screenshots for layout detection?#

Screenshots are deceptive. A screenshot of a mega-menu doesn't tell the AI if that menu is a

child of the nav bar or a React Portal rendered at the document root.

Because replay automatically detects complex spatial relationships over time, it can differentiate between these two architectural patterns. It watches the menu open. It sees if the rest of the page shifts (indicating a layout change) or if the menu floats above (indicating a new stacking context).

Industry experts recommend moving away from "guess-and-check" AI prompting toward "context-rich" generation. Replay provides this context. This is why AI agents like Devin and OpenHands use Replay’s Headless API to generate production code in minutes. They don't just get a "lookalike" UI; they get a functionally accurate component.

Example: Legacy HTML vs. Replay-Generated React#

Consider a legacy system where z-index was handled with "magic numbers" like

.

Legacy Code Snippet:

html
<!-- The "Spaghetti" approach Replay encounters -->
<div class="header" style="position:fixed; z-index: 100;">
  <div class="dropdown" style="z-index: 99999;"> 
    <!-- This often breaks in modern browsers -->
    <ul>...</ul>
  </div>
</div>

When replay automatically detects complex nesting like this, it doesn't just copy the bad code. It refactors it into a modern, scalable React structure using Radix UI or your internal design system.

Replay-Generated React:

tsx
import * as DropdownMenu from '@radix-ui/react-dropdown-menu';
import { styled } from '@/stitches.config';

// Replay extracts the exact brand tokens from the video
export const ModernHeader = () => (
  <HeaderContainer>
    <DropdownMenu.Root>
      <DropdownMenu.Trigger asChild>
        <Button>Options</Button>
      </DropdownMenu.Trigger>
      {/* Replay correctly identifies this as a Portal requirement */}
      <DropdownMenu.Portal>
        <DropdownContent sideOffset={5}>
          <DropdownItem>Edit</DropdownItem>
          <DropdownItem>Delete</DropdownItem>
        </DropdownContent>
      </DropdownMenu.Portal>
    </DropdownMenu.Root>
  </HeaderContainer>
);

How do I modernize a legacy system using Replay?#

Modernizing a system with $3.6 trillion in technical debt requires more than just a fresh coat of paint. You need to capture the behavior of the old system. The "Replay Method" follows a three-step process: Record → Extract → Modernize.

1. •Record: Use the Replay recorder to capture every state of your legacy application.
2. •Extract: Replay's Agentic Editor parses the video. Here, replay automatically detects complex layout hierarchies, z-index values, and even multi-page navigation flows.
3. •Modernize: Export the result as pixel-perfect React components.

This approach is particularly effective for Modernizing Legacy UI in regulated environments. Replay is SOC2 and HIPAA-ready, offering on-premise deployments for enterprise teams who cannot send their data to public AI clouds.

The Role of the Agentic Editor in Layout Precision#

Replay's Agentic Editor isn't just a text box. It is a surgical tool. When you need to swap out a legacy "Blue" for a new "Brand-Primary-600," the editor understands where that color sits within the layout hierarchy.

If the video shows a shadow depth that implies a specific z-index, the Agentic Editor ensures the generated CSS reflects that elevation. It uses "Search/Replace" logic with surgical precision, ensuring that a change in one component doesn't break the layout of another. This is how Replay turns a Prototype to Product faster than any manual workflow.

Handling Responsive Complexity#

Layouts change across screen sizes. A sidebar on desktop becomes a hamburger menu on mobile. Replay automatically detects complex responsive shifts by analyzing recordings across different viewport sizes. It identifies the "breakpoint" where a layout transitions from a

to a .

Instead of you manually writing media queries for 40 hours, Replay extracts these rules in 4. It sees the behavior, understands the intent, and writes the code.

typescript
// Replay extracts responsive layout logic from video context
const ResponsiveLayout = styled('div', {
  display: 'flex',
  flexDirection: 'column',
  gap: '$4',
  
  // Replay detected this breakpoint from the video recording
  '@tablet': {
    flexDirection: 'row',
    alignItems: 'center',
  },
  
  // Replay correctly identifies z-index requirements for the mobile overlay
  '@mobileOnly': {
    position: 'relative',
    zIndex: 50,
  }
});

Why Replay is the standard for Visual Reverse Engineering#

Replay is the first platform to use video for code generation. This isn't just a gimmick; it's a technical necessity. To truly understand a user interface, you must see it in its natural state—interacting with users.

Static screenshots lose the "Flow Map." A Flow Map is the multi-page navigation detection derived from video temporal context. Replay sees a user click a button, watches the loading state, and then observes the new page layout. It connects these dots to build a full application map, not just a single component.

For teams building AI-Driven Frontend Development pipelines, Replay's Headless API is the missing link. It allows AI agents to "see" the UI through Replay's lens, providing them with the high-fidelity data they need to write code that actually works in production.

Frequently Asked Questions#

What makes Replay different from "Screenshot-to-Code" tools?#

Screenshot-to-code tools are limited to a single static frame. They guess at hidden elements and depth. Replay uses video, which provides 10x more context. Because replay automatically detects complex z-index and layout shifts by watching elements move, the resulting code is much more accurate and requires significantly less refactoring.

Can Replay handle legacy systems with non-standard CSS?#

Yes. Replay is built for legacy modernization. It doesn't care if your source code is COBOL, jQuery, or a proprietary 20-year-old framework. If it can be rendered in a browser or captured on a screen, Replay can reverse-engineer it into modern React components and design tokens.

How does the Headless API work for AI agents?#

The Replay Headless API provides a REST and Webhook interface for AI agents like Devin. The agent sends a video recording to the API, and replay automatically detects complex UI structures, returning structured JSON or production-ready React code. This allows agents to build UI programmatically with human-level visual understanding.

Is Replay secure for enterprise use?#

Replay is designed for regulated environments. It is SOC2 and HIPAA-ready. For organizations with strict data sovereignty requirements, Replay offers On-Premise installations, ensuring that your UI recordings and source code never leave your private infrastructure.

Does Replay generate automated tests?#

Yes. One of the most powerful features of Replay is its ability to generate E2E tests. As it analyzes the video to create code, it also maps the user's interactions. It can automatically output Playwright or Cypress tests that mimic the exact flow captured in the recording, ensuring your new modern UI behaves exactly like the original.

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