Headline transparency

[iradex]

Hello guys, well, i'm using

local bg = CreateFrame("Frame", nil, f)
bg:SetBackdrop({
        bgFile = 'Interface\\ChatFrame\\ChatFrameBackground',
	edgeFile = 'Interface\\ChatFrame\\ChatFrameBackground',
	edgeSize = 1,
})
bg:SetBackdropColor(0, 0, 0, .4)
bg:SetBackdropBorderColor(0, 0, 0)
bg:SetFrameLevel(0)
bg:SetPoint("TOPLEFT", f, -1, 1)
bg:SetPoint("BOTTOMRIGHT", f, 1, -1)

on Stuf Unit Frames and Acb_castbar to set it transparency, and i'm trying to use it on Headline, buti can't find where to put the code, and the frame name. Need some help