For copyright, you can use the following code:

$(document).dolPopupAlert({
        message: _t('_copyright', (new Date()).getFullYear()),
        fog: {color:'#000', opacity:0.7}
    });

Instead of on_copyright_click function.

But it looks like we need to change fog by default for build-in dark mix:
https://github.com/unaio/una/issues/2720