numix-gtk-theme/gtk-3.0/scss/widgets/_window.scss

/**************
 ! Window frame
***************/

@include exports("window") {
	%window {
		box-shadow: 0 19px 38px rgba(0,0,0,0.30), 0 15px 12px rgba(0,0,0,0.22),
					0 0 0 1px $wm_border_focused;

		&:backdrop {
			box-shadow: 0 10px 20px rgba(0,0,0,0.19), 0 6px 6px rgba(0,0,0,0.23),
						0 0 0 1px $wm_border_unfocused;
		}
	}

	.window-frame {
		@extend %window;

		border: 0;
		border-radius: $roundness + 1;

		/* this is used for the resize cursor area */
		margin: $spacing * 3;

		&.tiled { border-radius: 0; }

		&.csd {
			&.popup {
				@extend %window;

				border-radius: 0;
			}

			&.tooltip {
				border-radius: $roundness;
				box-shadow: none;
			}

			&.message-dialog {
				@extend %window;

				border-radius: $roundness;
			}
		}
	}
}