Each layout customization requires custom steps, because each website is different (pay attention at some implementations presented under our
Gallery - there can't be a universal solution, because miniBB is designed to fit a lot of variations).
Your case is very simple I guess. You need to adjust colors and fonts modifying bb_default_style.css file (or implementing your own CSS, let's say, naming it bb_mksogn_style.css from the copy of our original sheet - but then don't forget to specify it under setup_options.php -> $skin setting). Adjusting colors means you change something, refresh the page and see what happens :-) Also analyze HTML code generated by forum program, to study the classes used in tables. I suppose, in your case you should just modify .gbody class to change the background color, then look up for 'font-family' and 'font-size' in CSS file to apply fonts.
Then you would modify
templates/main_header.html and
templates/main_footer.html,
copying HTML parts from your root page over them. Nobody can explain it since it's part of your experience, the same as nobody could give you instructions how to interact with a women you would like to build friendship with ;-)
All in all, if you prefer to see a practical example how this could be done in a couple of hours, just spend 2 Norway dinners price to pay our premium support fee, and avoid hours, if not days of work.