Steps to replicate the issue (include links if applicable):

• Set Math rendering mode to MathML
• Set font to Cambria Math
• Enter the expressions

\begin{pmatrix} 
   \begin{pmatrix}a&b\\c&d\end{pmatrix} & 
   \begin{pmatrix}e&f\\g&h\end{pmatrix} \\ 
    0 &
   \begin{pmatrix}i&j\\k&l\end{pmatrix} 
\end{pmatrix}

and

\det
  \begin{vmatrix} 
     c_0 & c_1 & c_2 & \ldots & c_n \\ 
     c_1 & c_2 & c_3 & \ldots & c_{n+1} \\ 
     c_2 & c_3 & c_4 & \ldots & c_{n+2} \\
     \vdots & \vdots & \vdots & & \vdots \\ 
     c_n & c_{n+1} & c_{n+2} & \ldots & c_{2n} 
  \end{vmatrix}>0

What happens?:

What should have happened instead?:

Rendered by Client Side MathJax

Rendered in LaTeX

Software version (on Special:Version page; skip for WMF-hosted wikis like Wikipedia):

Other information (browser name/version, screenshots, etc.):

Chrome: 129

Cause seems to be the padding around <mtd> elements.

the <mtd> padding rule highlighted in Developer Tools.
User agent style sheet rules are:

mtd {
    display: table-cell;
    text-align: -webkit-center;
    padding: 0.5ex 0.4em;
}

A problem we may not be able to do anything about.