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