Most of the “styles” are defined in the file menumacros.h. Basically what it does is it defines a heap of macros that accept parameters for building the UI components. Each macro contains definitions for the things like background style, background and foreground colours, borders and event related processing. You can easily modify the styles but hitting this file BUT if you are into wholesale changes then you might be better off recoding the menus from scratch. Lets you learn a lot. In a menudef you can group multiple entities together to give you a prefabricated control. You can also use calculatable macros to supply positioning relating information aling the lines of:
#define MENU_BUTTON_X(index) (index == 0) ? (BORDER_WIDTH) : ((2*BORDER_WIDTH)+LEFT_ITEM_WIDTH+(((BORDER_WIDTH+MENU_ITEM_WIDTH)*(index-1))))
#define MENU_BUTTON_WIDTH(index) (index == 0) ? (LEFT_ITEM_WIDTH) : (MENU_ITEM_WIDTH)