mediawiki-skins-Vector/resources/skins.vector.styles/components/PinnableElement.less

.vector-pinnable-element {
	.vector-menu {
		border-top: @border-width-base @border-style-base @colorGray14;
	}

	// Remove the border for the first .vector-menu since
	// it already exists on the pinnable header, or, when there's no
	// pinnable header, a border exists on the dropdown container.
	.vector-menu:first-child,
	.vector-pinnable-header + .vector-menu {
		border: 0;
	}
}