I use em units for measurement but you can use pixels if you prefer. EM’s are relative which works better for a responsive website, but and px are fixed dimensions. You can use http://www.pxtoem.com to convert px to em and vice versa.
Don’t forget to read up about WordPress child themes because if you plan to make core theme file modifications, and then make theme updates later, your changes will be lost. Also, please note that changes to the above containers may affect other parts of your website on other pages.
Oops! I just realized I posted this with my other user account instead of my Admin. Still, my answers would be the same B)