Dim unfocused windows

Set the opacity of application windows that are not focused:

gnoblin.window_rule {
    match = {type = "window", focused = false},
    opacity = 0.95,
}

focused = false matches windows that do not currently have focus. opacity is a number from 0 (transparent) to 1 (opaque); the example uses 0.95. The rule applies to windows, not layer surfaces.

Opacity affects text and controls too. For a translucent panel with opaque text, use transparency in the client's background instead. Remove this rule to inherit the previous matching opacity again.

See the window rule reference for all match fields and effect ranges.