Examples: The `USDZExporter button` is displayed incorrectly in `misc_exporter_usdz.html`

[linbingquan]

Description

three.js/examples/misc_exporter_usdz.html

Lines 34 to 36 in 67c4225

	<a id="link" rel="ar" href="" download="asset.usdz">
	<img id="button" width="100" src="files/arkit.png">
	</a>

The USDZExporter button is displayed incorrectly in misc_exporter_usdz.html, I think the arkit.png image transparency causes this problem.

Reproduction steps

1. Open https://threejs.org/examples/misc_exporter_usdz.html in browser.
2. We can't see the USDZExporter button in the middle at the bottom of the screen, but we can click it.

Code

three.js/examples/misc_exporter_usdz.html

Lines 34 to 36 in 67c4225

	<a id="link" rel="ar" href="" download="asset.usdz">
	<img id="button" width="100" src="files/arkit.png">
	</a>

Live example

https://threejs.org/examples/misc_exporter_usdz.html

Screenshots

Version

r155

Device

Desktop

Browser

Chrome, Firefox

OS

Windows

[Mugen87]

This examples is mainly intended for iOS where an icon automatically appears by the OS, see #23306. Hence, the example was updated such that a transparent button that triggers the export is behind the icon .