I cannot change the font size of package explorer in Eclipse

Question

I try to change the font size of package explorer in Eclipse from menu Window → Preferences → General → Appearance, and I fail to change

Answer 1

Thanks to Veger's reply, I successfully changed the font of my PHP Explorer in PHP Perspective (with PDT installed). The following CSS code,

    #org-eclipse-php-ui-explorer Tree {
       font-family: Consolas;
       font-size: 21px;
    }

are added into my "eclipse-4.3\plugins\org.eclipse.platform_4.3.1.v20130911-1000\css\e4_default_win7.css" file.

You may choose a different CSS file, depending on the theme you choose through Preferences → General → Appearance: "Theme" drop-down list).