title: Increase font size in Qt
body: <p>I have a GUI with some math symbols that might be hard to read at the default font size, so I would like to create a <code>QFont</code> object that has a size of <code>system_default+4</code>.</p>
  
  <p>However, there doesn't seem to be a way to get the default size in the first place, and I don't want to hardcode a size that might be even smaller than what the user is using.</p>