The text in help page do not display properly after zooming.

As the topic said, when I zoom the help page to 120% or 150% (use Ctrl + mouse wheel), some words in the text seems kinda abnormal. In one word, the gap between two letters just seems tow close or too far.  Please see the pic, zooming is 150%, the text font is Arial, text style is regular, text size is 12.

And another problem is that the text font in help page is always Arial not matter how I changed the font setting by changing the setting in Tools -> Options -> Help -> Font -> Family/Style/Size。