PortableInfobox/styles/PortableInfoboxMonobook.scss

// fix issues with default infobox styles on monobook
$background-color: #f9f9f9;
$background-color-secondary: #e5e5e5;

.portable-infobox {
	background-color: $background-color;

	figure {
		margin: 0;
	}

	.pi-secondary-background {
		background-color: $background-color-secondary;
	}
}