fix/bug#1233-iframe-overlap-issue

[Niveditarani]

This PR fixes the bug#1233- iframe overlap issue.

CSS property overflow: hidden at the parent container was interfering with the layout calculations and was forcefully clipping child elements. Making the resize div to float beside the iframe instead of overlapping.

Before:

After fix:

[CLAassistant]

All committers have signed the CLA.

[KernelDeimos]

I recorded a manual test. (Usually I speed these up to make the file smaller, but I decided to try compressing it this time - text on screen is a little distorted but it doesn't seem to affect legibility too much.)

I noticed this fix causes a new problem: window border radius is not rendered as expected. The titlebar background is able to clip out of the window area because overflow: hidden was removed.

We need to find a way to solve this CSS bug, but also preserve the window border radius.

This was a very good thing to try; it's good for us to know how these things are intertwined.

pr-1250_compressed.mp4

[Niveditarani]

overflow: hidden property in the parent container was enforcing strict containment- making child elements to respect the parent's geometric boundaries (including border- radius).

Now without this property, children will naturally overflow their parent's boundaries including overflowing past rounded corners. So the border-radius wasn't actually removed - it was just being masked by overflowing content, breaking expected visual boundaries (e.g., titlebar background escaping the border-radius).

This commit replaces overflow: hidden with contain: paint, which maintains a clipping boundary similar to overflow: hidden, but without affecting layout flow—allowing the resize div to properly overlap the iframe instead of floating beside it.

[KernelDeimos]

Thanks! I was able to test locally with JSONEditor added in my Dev Center and that's working better, everything else looks good too.