Setting stylesheet breaks consistency between platforms

Reproducer attached. It's a QCalendarWidget embedded in a QWidget and manged by QVHoxLayout. The problem is that the rendering result is different on desktop (say Windows or Linux) and on WASM. This is how it looks on desktop:

Although it is little weird already (text in quite many cells are elided), all of cells are rendered. But this is how it looks on WASM:

Many cells are just empty.

I assume it is stylesheet breaking the size hints and/or layout somehow. Since everything works just fine if you comment out

QString style = QString::fromStdString(szCss);

Or, you can also give the main QWidget a larger size, i.e. uncomment

main->resize(main->size() * 2);

So my rough guess is that the style (especially those defined in pixels) may confuse widget sizing somehow.