Round application windows

Set the corner radius and smoothing for application windows:

gnoblin.window_rule {
    match = {type = "window"},
    corners = {radius = 14, smoothing = 0.6, mode = "auto"},
}

Field	Accepted values	Default	Effect
radius	Number from 0 to 200 logical pixels	0	Sets the requested corner radius.
smoothing	Number from 0 to 1	0	Adjusts the corner curve.
mode	"auto", "force", or "off"	"auto"	Preserve existing client corners, force a mask, or disable masking.

The example uses "auto" to preserve existing client corners. See window effects for state exceptions and how to force a mask deliberately.