Changing background colour from #ffffff to #f6f6f6

I have the same concern. Where is the main front-end CSS file?

I was thinking to make some padding, margings, font style and size changes but I couldn’t find CSS file to edit.

Hi.
Admin.css is only for administration settings in WordPress Settings.

You must edit file class-floating-social-bar.php.
Change make in section #fsb-social-bar, here is: background: #fff. I set this value to transparent: background: rgba(0, 0, 0, 0), but around button is still visible little white border. See the image: https://docs.google.com/file/d/0Bywu71F_pzISV1ZpSkFZU3lERDQ/edit?usp=drivesdk

change border to 0 hide, or/and like color

`border-bottom: 1px solid #000; border-top: 1px solid #000;

One pixel line I want top and down, this is correct, but I mean background around social buttons.