Context menu dialog "Show Math As > TeX Commands" misaligned vertically

Issue Summary

When selecting Show Math As > TeX Commands from the MathJax contextual menu on a rendered equation, the resulting dialog window opens incorrectly anchored to the very top edge of the browser viewport instead of being centered on the screen.

Host Page: https://www.mathjax.org/#demo

Browsers tested: Chrome v151.0.7922.76

OS: Windows 11

Steps to Reproduce:

1. Navigate to the MathJax Live Demo page.
2. Right-click any rendered equation and select Show Math As > TeX Commands.
3. Observe the layout positioning of the appearing source dialog window.

Expected behavior:
The dialog window centers vertically on the screen.

Actual Behavior:
The dialog window sticks to the very top edge of the screen.