For this demonstration we will replace the Human UI, but you can do this for all the races:
1. Import all files except "blank.dds".
2. Rename the files:
"ui\console\human\humanuitile-inventorycover.dds"
"ui\console\human\humanuitile-timeindicatorframe.dds"
"ui\console\human\humanuitile01.dds"
"ui\console\human\humanuitile02.dds"
"ui\console\human\humanuitile03.dds"
"ui\console\human\humanuitile04.dds"
"ui\widgets\console\human\human-console-button-back-active.dds"
"ui\widgets\console\human\human-console-buttonstates2.dds"
"ui\widgets\escmenu\human\human-options-button-highlight.dds"
"ui\widgets\escmenu\human\human-options-menu-background.dds"
"ui\widgets\escmenu\human\human-options-menu-border.dds"
"war3mapImported\Black Box.tga"
3. Import "blank.dds" rename it to "ui\console\human\humanuitile05.dds"
4. Import "blank.dds" again and rename it to "ui\console\human\humanuitile06.dds". These two UI frames are those that extend to the left and right of the screen on classic graphics.
5. Lastly we will hide the default black screen on the bottom and replace it with our own "Black box.tga" so it covers the portait on the backside. This requires a few lines of code shown below.
Code:
function Setup takes nothing returns nothing
local framehandle blackbox
call BlzFrameSetVisible(BlzGetFrameByName("ConsoleUIBackdrop",0), false) // Hide bottom black box
set blackbox = BlzCreateFrameByType("BACKDROP", "", BlzGetOriginFrame(ORIGIN_FRAME_GAME_UI, 0), "", 0) // tiny black box behind portrait
call BlzFrameSetSize(blackbox, 0.1, 0.15)
call BlzFrameSetAbsPoint(blackbox, FRAMEPOINT_CENTER, 0.25, 0.05)
call BlzFrameSetTexture(blackbox, "war3mapImported\\Black box.tga", 0, true)
call BlzFrameSetLevel(blackbox , -1)
endfunction