Why the font size won't change with browser zoom in?

The problem is that you have set -webkit-text-size-adjust: none; for the body in layout.css. Changing it to -webkit-text-size-adjust: auto; allows the zooming of the fonts along with the page.

Edit: Corrected the CSS. Should be auto not 0

Fonts using a specific pixel size are not relative (along with several others). Zooming changes that relative information.

From http://www.westciv.com/style_master/academy/css_tutorial/properties/values.html

Name        Abbrev. Explanation                             Relative?em          em      The height of a font                    yesex          ex      The height of the letter x in a font    yespica        pc      1 pica is 12 points                     nopoint       pt      1/72 of an inch                         nopixel       px      One dot on a screen                     nomillimeter  mm      Printing unit                           nocentimeter  cm      Printing unit                           noinch        in      Printing unit                           no

If you're using a fixed-point width for your font-size settings (e.g.: pixels), then your font size will remain unchanged when the user zooms. If you want the font to enlarge or diminish when the user zooms in/out, then consider using em as your unit (1 em = 100% of the default font size on the user's machine).