What is This Weird Font Bug??

Have you noticed that bright fonts against darker background look a bit bold and does not rendered correctly? I tried this on different computers, and I get the same results. This only happens on fonts on the internet; on a PDF the fonts look fine. See for yourself on this public Gdoc: 

The first font is Comfortaa, by Google Web fonts, the other one though is good old Arial. 

https://docs.google.com/document/d/13tpZy1jS1qNv-O8ulEekqJdAI_1pVD7zyy7lDVsO4UQ/edit

edit: 
A few weeks ago, I did not have this problem. I took a screen capture. Now when I put them next to each other, you can see the difference. This problem was NOT there all the time. Take a look for yourself, I added the screen capture to the doc below.