[spiel2001]

Edit [ Interface > AddOns > nUI > Bars > nUI_ButtonBars.lua ] and locate the following section then comment out the part I highlighted. That should do the trick.

function nUI_ButtonBars:createBar( name, layout )
    
--    nUI_ProfileStart( ProfileCounter, "createBar" );
    
    local bar  = CreateFrame( "Frame", name, nUI_Dashboard.Anchor, "SecureHandlerStateTemplate" );
    bar.events = CreateFrame( "Frame", name.."_Events", nUI_ButtonBars );
    bar.layout = layout;
--[[    
    bar:SetBackdrop(
        {
            bgFile   = "Interface\\AddOns\\nUI\\Layouts\\Default\\Art\\nUI_BevelboxBg.blp", 
            edgeFile = "Interface\\AddOns\\nUI\\Layouts\\Default\\Art\\nUI_BevelboxBorder.blp", 
            tile     = true, 
            tileSize = 1, 
            edgeSize = 12, 
            insets   = {left = 0, right = 0, top = 0, bottom = 0},
        }
    );
    
    bar:SetBackdropColor( 0, 0, 0, 0.35 );
]]--