[Baertram]

Hi Robert,

you can try to use this virtual backdrop here, it looks black see-through with a small thin border around it:

<GuiXml xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:noNamespaceSchemaLocation="http://sir.insidi.at/or/schema/esoui.xsd">
<Controls>
		<Backdrop name="DarkThinFrameBackdrop" inherits="ZO_DarkThinFrame" virtual="true" tier="LOW" layer="BACKGROUND" level="0">
			<Anchor point="TOPLEFT" offsetX="-4" offsetY="-4"/>
            <Anchor point="BOTTOMRIGHT" offsetX="4" offsetY="4"/>
            <Edge file="EsoUI/Art/Miscellaneous/dark_edgeFrame_8_thin.dds" edgeFileWidth="64" edgeFileHeight="8" />
            <Center file="EsoUI/Art/Miscellaneous/Gamepad/gp_edgeFill.dds" />
        </Backdrop>



</Controls>

</GuiXML>

Then create a TopLevelControl and at it's <Controls> add this e.g.

<TopLevelControl name="MyUI_TLC_Keyboard">
            <Dimensions x="900" y="600"/>
            <DimensionConstraints minX="900" minY="600"/>
            <Anchor point="CENTER" relativeTo="GuiRoot" relativePoint="CENTER" offsetX="0" offsetY="0"/>
<!-- Background -->
		    	<Backdrop name="$(parent)BG" alpha="1" inherits="DarkThinFrameBackdrop" centerColor="666666">
		    		<AnchorFill/>
				</Backdrop>

  </Controls>
        </TopLevelControl>

I bet there also is an easy way to craete just a plain black backdrop but I never did, so I'm not quite sure how to do it.
Maybe you can change the above line
<Backdrop name="$(parent)BG" alpha="1" inherits="DarkThinFrameBackdrop" centerColor="666666">
to use 000000 as center color.


Edit:
The ZO_DarkThinFrame backdrop with centerColor="666666" looks like this