Temporary iframe creation causes visible scrollbar flicker when generating large PDFs

[wabualhi]

When using dom-to-image-more to generate a PDF (especially from large DOM elements), the library temporarily creates an <iframe> in the document.
This iframe becomes briefly visible, which causes a vertical scrollbar to appear on the screen for a moment before it is removed.

This results in a small but noticeable layout shift (flicker) during PDF generation.

Steps to Reproduce:

Use dom-to-image-more.toPng() or .toJpeg() on a large DOM element.

Generate a PDF using jsPDF or similar.

Observe the page while the process runs.

You’ll see a vertical scrollbar appear briefly, then disappear after the process finishes.

Expected Behavior:
The temporary iframe used internally for rendering should not affect the visible layout —
it should be created off-screen or hidden (position: fixed; top: -9999px; visibility: hidden;).

Actual Behavior:
A visible scrollbar appears briefly while the iframe exists.

"dom-to-image-more": "^3.7.1",

[IDisposable]

As you can see, we do create it hidden and static positioned, but not off-screen. PR welcome

dom-to-image-more/src/dom-to-image-more.js

Lines 1470 to 1477 in ca6ff28

	// Create a hidden sandbox <iframe> element within we can create default HTML elements and query their
	// computed styles. Elements must be rendered in order to query their computed styles. The <iframe> won't
	// render at all with `display: none`, so we have to use `visibility: hidden` with `position: fixed`.
	sandbox = document.createElement('iframe');
	sandbox.id = 'domtoimage-sandbox-' + util.uid();
	sandbox.style.visibility = 'hidden';
	sandbox.style.position = 'fixed';
	document.body.appendChild(sandbox);