Clicking To easily change the Background Decal button allows you to select an image to use as a the decal in the center of the Fantasy Grounds desktop. This :
Click on the Options icon in the Sidebar.
Click the Backgrounds Decal button at the bottom of the Options window.
Select the Decal you would like to use.
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The Background Decal you select will remain under all windows popped up in Fantasy Grounds UnityVTT.
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The Search field (denoted by a magnifying glass icon) allows you to search for keywords associated with the image you wish to use.
To remove a selected decal, click the Clear button Use Empty Decal button at the bottom of the Select Decal window.