mathbackground does not cover the expression's background

[pkra]

For example

<math xmlns="http://www.w3.org/1998/Math/MathML">
  <mstyle mathbackground="red">
      <mn>1</mn>
  </mstyle>
</math>

Renders as

in mj3-demos, i.e., the background color is not filling the content's background, only a thin part at the bottom.

When I add

mjx-math * {
    background: inherit;
}

it looks ok but I'm not sure if that has side effects.

[dpvc]

It looks like the CSS

mjx-mstyle {
  display: inline-block;
}

is missing. I thought these were added automatically for all the node types, but I will check the code to see what is happening.