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html2canvas does not take a pixel-perfect screenshot of the browser tab. It rebuilds an image from the DOM and the style information it supports. A layer that appears on top in Chrome, Firefox, or Safari can therefore be painted behind another layer in the canvas. Fix the problem by isolating the overlap, checking stacking contexts and supported CSS, reasoning through html2canvas’s paint order, and applying a capture-only adjustment with onclone. If the output must match the browser’s actual pixels, use a native browser capture API or a headless-browser workflow instead.
Why is z-index not working in html2canvas?
A CSS z-index value is meaningful only inside the stacking context that contains the element. An element with z-index: 999999 can still appear below an element in a different ancestor context. html2canvas adds another constraint: it classifies DOM nodes and paints them itself rather than asking the browser for the already-composited tab image.
The project documentation describes CSS support as property-by-property and incomplete. Its FAQ puts the limitation plainly: “Every CSS property must be manually implemented to render correctly, so html2canvas will never have full CSS support.” Consequently, increasing a number is not a universal fix. The mismatch may come from an unsupported property, an unexpected stacking-context boundary, or the renderer’s handling of descendants.
Reproduce the mismatch with a minimal case
Start with only the two overlapping elements and the styles that affect them. This prevents unrelated transforms, opacity, filters, and positioned ancestors from hiding the real cause.
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<div id="stage">
<div class="panel">Panel</div>
<div class="badge">Badge should be on top</div>
</div>
<style>
#stage { position: relative; width: 420px; height: 220px; }
.panel { position: absolute; inset: 20px; z-index: 1; background: steelblue; }
.badge { position: absolute; top: 35px; left: 40px; z-index: 2; background: gold; }
</style>
<script>
html2canvas(document.querySelector('#stage')).then(canvas => {
document.body.appendChild(canvas);
});
</script>Compare the live page and the generated canvas. Record which node is visually wrong, which ancestor establishes its stacking context, and whether the discrepancy occurs only after a transform, opacity, filter, or other effect is applied.
Inspect stacking contexts before changing z-index
Use browser developer tools to walk from each overlapping element to the root. Look for ancestors with properties that establish a new stacking context, including positioned elements with a non-auto z-index, transforms, opacity below 1, filters, isolation, and related compositing rules. Two descendants in different contexts cannot be reordered by changing their local numbers alone.
Questions to answer for both elements
- Are they positioned, and are their
z-indexvalues applied to the elements you think they are? - Do their nearest stacking-context ancestors differ?
- Does an ancestor clip the element with
overflowor establish a new containing block? - Are transforms, opacity, filters, or isolation creating an additional context?
- Is one node in normal in-flow content while the other is positioned?
As a diagnostic, temporarily remove transforms, opacity, filters, and ancestor z-index values. If the canvas then matches, restore the rules one at a time and identify the declaration that changes the result. Keep this test separate from the final design; it is meant to locate the boundary.
Understand html2canvas’s paint order
The renderer source organizes a stacking context into ordered phases. The implementation currently paints the context’s background and borders, then negative stack-level children, in-flow content and non-inline descendants, floats and inline-level descendants, positioned/opacity/transform descendants with auto or zero stack levels, and finally positive z-index stacking contexts in z-index order.
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Negative values need special care
A negative stack level is painted before in-flow content in the renderer’s sequence. An element moved to z-index: -1 can consequently disappear behind its context’s background or other content. Use negative values only when that ordering is intentional, and test the canvas rather than inferring the result from the browser view.
Positive values are local, not global
Positive stack levels are ordered after the earlier phases, but only among contexts that are being compared at that level. A child with z-index: 100 cannot escape an ancestor context that is painted below a sibling context. Move the stacking-context boundary, not merely the child’s number, when that is the cause.
Check whether the CSS is supported
html2canvas implements CSS properties manually. The official FAQ asks users to prepare a reduced test case when a property is missing or incomplete. Check the project’s supported-features documentation and test the smallest possible page. Features that affect compositing or painting deserve particular suspicion.
- Replace an advanced effect with a plain positioned box and background. If ordering becomes correct, the effect may be unsupported or partially supported.
- Remove
transform,filter, opacity, clipping, and pseudo-element dependencies one at a time. - Make key geometry explicit with
position,top/left, width, height, and a background while debugging. - Verify that the element is present in the cloned document and is not hidden by a selector or a loading state.
Use onclone for a capture-only fix
The onclone option receives the cloned document that html2canvas is about to render. You can alter that clone without changing the live page seen by users. This is the safest place for a screenshot-specific stylesheet, a simplified effect, or a temporary stacking arrangement.
Example: move an overlay into a controlled capture layer
const target = document.querySelector('#stage');
html2canvas(target, {
onclone: (clonedDocument) => {
const clonedStage = clonedDocument.querySelector('#stage');
const clonedBadge = clonedDocument.querySelector('.badge');
if (!clonedStage || !clonedBadge) return;
clonedStage.style.position = 'relative';
clonedStage.style.isolation = 'isolate';
clonedBadge.style.position = 'absolute';
clonedBadge.style.zIndex = '10';
clonedBadge.style.transform = 'none';
clonedBadge.style.filter = 'none';
}
}).then(canvas => {
document.querySelector('#output').replaceChildren(canvas);
});This does not make an unsupported feature supported. It gives the renderer a simpler, explicit arrangement for the capture. Keep the callback narrowly scoped: changing global selectors, dimensions, or content can create a different screenshot than intended.
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Example: inject a temporary stylesheet
html2canvas(document.querySelector('#stage'), {
onclone: (doc) => {
const style = doc.createElement('style');
style.textContent = `
#stage { isolation: isolate !important; }
#stage .background { position: absolute !important; z-index: 0 !important; }
#stage .foreground { position: absolute !important; z-index: 1 !important; }
#stage .problem-effect { transform: none !important; filter: none !important; }
`;
doc.head.appendChild(style);
}
});Use !important only in this temporary stylesheet when existing author rules otherwise win. Remove each override after you have confirmed which one fixed the ordering, then keep the smallest working change.
When html2canvas is the wrong capture technology
If the requirement is “the exact pixels in the browser tab,” switch tools instead of endlessly tuning CSS. The html2canvas FAQ points browser-extension authors to the browser’s native screenshot API. For server-side capture, it names Puppeteer and Playwright, which drive a real (usually headless) browser and capture its rendered page.
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1Repair Windows errors before they cause bigger problems2Scan for outdated or missing drivers - takes under a minute3Clear out junk files and repair common Windows errors| Requirement | Approach | Why |
|---|---|---|
| Selective DOM rendering, with a canvas you can post-process | html2canvas | Convenient in-page reconstruction, but CSS support is incomplete and output can differ from the tab. |
| Extension screenshot of the current tab | Native browser tab-capture API | Captures the browser’s rendered tab rather than rebuilding it from DOM data. |
| Server-side screenshot of a URL | Puppeteer or Playwright | Drives a browser for full-page rendering and screenshot capture. |
| Managed API with cleanup, retries and formats | ScreenshotNeo | One request returns PNG, JPEG, WebP or PDF; it removes common consent UI before capture and reports billing status. |
Or skip the browser setup
For a URL screenshot, ScreenshotNeo provides a hosted endpoint and an MCP server for Claude, Cursor, and other MCP clients. The request below captures Stripe as WebP:
curl -G "https://api.screenshotneo.com/v1/shot" -d access_key=YOUR_API_KEY --data-urlencode url=https://stripe.com -o shot.webpSee the ScreenshotNeo documentation for all options and response headers. It can load lazy images for full-page captures, target one CSS selector, emulate dark mode and 12 device presets, set any viewport and retina scale, generate PDFs with paper size, margins, orientation and page ranges, render HTML/CSS, run custom JavaScript, click an element, wait for a selector, delay or network idle, hide selectors, block ads/trackers/requests/resource types, send headers/cookies/user agents/Authorization, set timezone or geolocation, use transparent backgrounds, resize images, cache with your chosen TTL, create signed links, submit async jobs with signed webhooks, capture up to 100 URLs per call, expose usage data, and provide an OpenAPI specification. Parameter names used by other screenshot APIs also work.
Cookie banners, newsletter popups and chat widgets are removed before the shot. Bot checks, blank pages and failed loads are not billed, and response headers identify the page verdict and billing status. The MCP tools are take_screenshot, get_page_info and capture_pdf. The Free plan includes 1,000 screenshots a month with no card; paid plans start at $5 for 3,000. Create a free ScreenshotNeo account.
Troubleshooting checklist
The higher z-index has no effect
Check whether the elements are in different stacking contexts. Move the value to the ancestor context being compared, or use onclone to create a single isolated capture context.
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The browser is correct but the canvas is wrong
Reduce the page, remove compositing effects, and verify CSS support. If a simplified version works, replace or flatten the unsupported effect for capture.
An element vanishes from the canvas
Confirm it exists in the cloned document, is not hidden by a selector, has non-zero dimensions, and is not clipped by an ancestor. Temporarily give it an opaque background and explicit size.
Only fonts or images differ
Wait until resources are ready before calling html2canvas, and verify that cross-origin resources are configured for canvas use. A resource failure can make the result look like a layering error even when the paint order is correct.
The fix changes the live page
Move all diagnostic styles into onclone. Do not mutate the original nodes before capture unless the visual change is intended for users.
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Server capture is blank or times out
Use a browser-driven workflow or a managed API, wait for the page’s readiness condition, and inspect the returned status. For ScreenshotNeo, the X-Page-Verdict and X-Billed headers distinguish clean captures from bot checks, blank pages, timeouts, failed loads and cache hits.
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Performance, reliability and cost considerations
html2canvas runs in the page and must traverse and paint the selected DOM. Capture a smaller element when full-page output is unnecessary, avoid repeated captures during animation, and wait for stable layout before invoking it. Clone-only simplifications can reduce work as well as improve ordering.
Native and headless-browser captures use more browser infrastructure but are the appropriate trade-off for pixel fidelity. A hosted service can remove that setup and add waiting, blocking, caching and asynchronous jobs. ScreenshotNeo bills only clean shots; bot checks, blank pages, timeouts, failed loads and cache hits cost nothing. Its plans are Free (1,000 per month), Starter $5 for 3,000, Growth $15 for 15,000, Pro $39 for 60,000, Scale $99 for 250,000, and Business $249 for 1,000,000; yearly billing gives two months free, and every feature is on every plan.
Decision guide
- Choose html2canvas when you need a browser-side, DOM-selective canvas and can accept that supported CSS determines the result.
- Choose a native extension API when you need the current tab’s actual rendering.
- Choose Puppeteer or Playwright when your server must drive a browser and retain control of the environment.
- Choose ScreenshotNeo when you want a URL-to-image or PDF endpoint, cleanup of consent and overlay UI, usage headers, bulk or asynchronous capture, or MCP tools for AI agents.
Frequently Asked Questions
Can I solve every html2canvas layering bug with a larger z-index?
No. z-index is scoped to stacking contexts, and html2canvas may not support or classify the CSS involved the same way as the browser.
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No. It modifies the cloned document used for that capture. Keep the callback focused so the screenshot-only variant remains predictable.
Which tool should an extension use for an exact tab screenshot?
Use the browser’s native screenshot or tab-capture API, as recommended by the html2canvas FAQ.
Which hosted ScreenshotNeo tool is used for PDFs?
The MCP server exposes a tool named capture_pdf, while the HTTP endpoint also supports PDF output and PDF options.
The Bottom Line
First verify stacking contexts and supported CSS, then simplify the clone with onclone. If “correct” means the browser’s actual pixels rather than a DOM reconstruction, use native tab capture, Puppeteer, Playwright, or ScreenshotNeo.
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