When using make4ht with mjcli to render Mathjax upfront, closing braces are not rendered at all.

I have attached a minimal example. When I compile this with `make4ht -f html5+mjcli mjcli_test.tex "mathjax"` the browser shows "Test: {1,2,3" instead of "Test: {1,2,3}".

I think the reason for this is the code that extracts the Mathjax CSS from the HTML files. mjcli creates the record

mjx-c.mjx-c7D::before {
padding: 0.75em 0.5em 0.25em 0;
content: "}";
}

the CSS file generated by make4ht (mjcli_test-mathjax.css), however, only contains the record

mjx-c.mjx-c7D::before {
padding: 0.75em 0.5em 0.25em 0;
}

The `parse_css` function in make4ht-mjcli.lua uses `if line:match("%}") then` to detect if a line marks the end of a record. I think this matches the 'content...' line and the record is not completely red.