custom css can be added in Theme options > Layout > Custom CSS & JS > Custom CSS section. Also you can add custom css for pages in "Page options" section while you create/edit page.
If css from "Page options" does not work for blog page, then of course you can use Theme options > Layout > Custom CSS & JS > Custom CSS section instead. Each css should start then with .blog class or .single-post class if page is single post page. More information about customizations via Firebug you can read at http://themes.muffingroup.com/betheme/documentation/#theme-customizations
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custom css can be added in Theme options > Layout > Custom CSS & JS > Custom CSS section. Also you can add custom css for pages in "Page options" section while you create/edit page.