STYLES:

There are two style tables - first is button styles, second is window styles.

A buttonstyles table entry:

[2] = {
     name = "Blue",
     image = "gfx/mybuttonimage.png",
     hover = "gfx/mybuttonimagehover.png",
     click = "gfx/mybuttonimageclick.png",
     sizex = 64,
     sizey = 32,
     txtr = 255,
     txtg = 255,
     txtb = 255,
     ox = -32,
     oy = -8,
}

name - the style name. Not used anywhere, is there only for recognition
image - the image of an inactive button
hover - the image of a hovered button
click - the image of a clicked button
sizex - x size (width) of the image
sizey - y size (height) of the image
txtr - R of the hudtxt caption's RGB color
txtg - G of the hudtxt caption's RGB color
txtb - B of the hudtxt caption's RGB color
ox - x offset of the hudtext caption (sizex/-2)
oy - y offset of the hudtext caption (rounded sizey/-3.8)



A windowstyles table entry:

[2] = {
     name = "Grey",
     image = "gfx/sprites/block.bmp",
     sizex=32,
     sizey=32,
     bgr=155,
     bgg=155,
     bgb=155,
     brr=210,
     brg=216,
     brb=221,
     txtr=255,
     txtg=255,
     txtb=255,
     hlr=0,
     hlg=0,
     hlb=174,
}

name - the style name. Not used anywhere, is there only for recognition
image - the image of the content area and borders
sizex - x size (width) of the image
sizey - y size (height) of the image
bgr - R of the content area background's RGB color
bgg - G of the content area background's RGB color
bgb - B of the content area background's RGB color
brr - R of the headline background's RGB color
brg - G of the headline background's RGB color
brb - B of the headline background's RGB color
txtr - R of the text inside the window RGB color (unused)
txtg - G of the text inside the window RGB color (unused)
txtb - B of the text inside the window RGB color (unused)
hlr - R of the headline text's RGB color
hlg - G of the headline text's RGB color
hlb - B of the headline text's RGB color

Welcome screen as seen in the video preview:
You can put it in any hook, it's just functions.
Note: the Welcome window example uses a second style for the button which was implemented manually and is not and won't be in the final release.