Fullscreen image viewer UI scales incorrectly when browser zoom is below 100%

What issue are you seeing?

The fullscreen image viewer UI is incorrectly scaled on desktop when browser zoom is below 100%.

When opening an image in fullscreen mode, the interface appears oversized and does not properly adapt to the current browser zoom level.

This is especially noticeable with screenshots or large preview images, such as iPhone simulator screenshots.

What steps can reproduce the bug?

1. Open ChatGPT/Codex on desktop.
2. Set browser zoom below 100% (for example 80% or 67%).
3. Open an image generated or displayed in chat.
4. Click the image to open it in fullscreen mode.
5. Observe that the fullscreen viewer UI appears incorrectly scaled.

What is the expected behavior?

The fullscreen image viewer UI should scale correctly and adapt to the current browser zoom level, even when the browser is below 100% zoom.

Additional information

The issue appears related to the fullscreen image modal or overlay not respecting the browser zoom scaling factor.

Tested on desktop browsers with zoom levels below 100%.