Qt4 documentation isn't rendered properly

While Qt Assistant from Qt 5.6.2 renders Qt4 documentation acceptable well, integrated help of QtC renders function declarations so small that it is very difficult to click on a function to get to its description. Zooming in doesn't change text size for normal text but only for titles.

This is most probably a Qt5.8 issue but I thought it should first be reported to QtC. Feel free to convert it to a QTBUG or let me know how documentation is rendered in QtC (QTextBrowser, QtWebEngine, something else) so that I can file it properly.