Text box color and font, Top Menu font

Hello,

First, I will admit that I am a complete beginner at all of this!

I have a few ‘basic’ questions.
1. I want to change the color of the grey text box that comes standard in the fifteen theme. Do I do this thru Appearance -> Editor? Once there, which section of code controls the color? I’ve tried changing multiple colors throughout the code, but none of them seem to be for this grey text box (in fact, I don’t see any changes at all!). I also want to change the font, but I do not know which section controls this font.

2. For the Primary Menu (e.g., Home, About us, etc.) on the header, I want to change the font to make it bold and larger. Again, I don’t know where to do this.

3. Somehow I managed to add a FB icon as part of the header. How do I delete this?

The site is rosieloudesigns.com

I apologize for these very beginner questions and any help is greatly appreciated!