Looks like set CSS style > "font-size" doesn't affect the TextBox object at all. "color" and "border" does.
Windows 7 64-bit Chrome/Firefox/IE
Not a bug: you have 'auto font size' set to 'Yes', which will override the font size.
Develop games in your browser. Powerful, performant & highly capable.
Of course... Sorry for posting "bugs" all the time;)