Fix default font on Windows

[StevenLu2004]

I was a MacOS user, and the default font of fman used to work fine for me. I switched to Windows lately, but the font was not loaded; instead, fman showed me a very ugly default font. I checked the original fman-users/Core repo and used the "Theme (Windows).css" as my template for custom CSS, and I found that Roboto works, whereas "Roboto Bold" doesn't (because Qt misinterprets it as the font's name, not the name and style); then I tried "font-weight: bold" with "font-family: Roboto" and achieved desired results. See images below.

[mherrmann]

I appreciate the PR; But it changes the fonts in a bad way. The fonts shouldn't be bold. Without your change, my fman looks as follows:

With your change, it looks as follows:

Removing font-weight: bold doesn't change this; The fonts are still rendered bold.

I believe you are experiencing something that's very particular to your system. I think it should be fixed on your system, not in fman itself because neither I nor to my best knowledge other people are experiencing it.