Variable: window-system-default-frame-alist

Window-system dependent default frame parameters.
The value should be an alist of elements (WINDOW-SYSTEM . ALIST),
where WINDOW-SYSTEM is a window system symbol (see `window-system')
and ALIST is a frame parameter alist like `default-frame-alist'.
Then, for frames on WINDOW-SYSTEM, any parameters specified in
ALIST supersede the corresponding parameters specified in
`default-frame-alist'.