Unfortunately none of the options to customize the appearance of the main window can be found ingame. They are only available to you if you know how to use an editor to open the Config.lua file, found in the addon folder. And that is what you will find there:
-- SETTINGS
local s = {
pos = { "TOPLEFT", 4, -4 },
width = 280,
maxlines = 9,
titleheight = 16,
titlefont = [[Fonts\ARIALN.TTF]],
titlefontsize = 13,
titlefontcolor = {1, .82, 0},
lineheight = 14,
linegap = 1,
linefont = [[Fonts\ARIALN.TTF]],
linefontsize = 11,
linetexture = [[Interface\Tooltips\UI-Tooltip-Background]],
linefontcolor = {1, 1, 1},
}