wp-calypso/client/reader/components/reader-popover/style.scss

.reader-popover.popover .popover__inner {
	background-color: var(--color-neutral-0);
	border-color: var(--color-neutral-10);
}

// Popover arrows
.reader-popover.popover.is-top .popover__arrow,
.reader-popover.popover.is-top-left .popover__arrow {

	&::before {
		border: 10px solid var(--color-neutral-0);
		border-bottom: none;
		border-left-color: transparent;
		border-right-color: transparent;
		border-top-style: solid;
		content: " ";
		margin-left: -10px;
		position: absolute;
		bottom: 2px;
		left: 50%;
	}
}

.reader-popover.popover.is-bottom .popover__arrow,
.reader-popover.popover.is-bottom-left .popover__arrow,
.reader-popover.popover.is-bottom-right .popover__arrow {

	&::before {
		border: 10px solid var(--color-neutral-0);
		border-bottom-style: solid;
		border-left-color: transparent;
		border-right-color: transparent;
		border-top: none;
		content: " ";
		position: absolute;
		left: 50%;
		top: 2px;
	}
}

.reader-popover.popover.is-left .popover__arrow,
.reader-popover.popover.is-left-top .popover__arrow {

	&::before {
		border: 10px solid var(--color-neutral-0);
		border-bottom-color: transparent;
		border-right: none;
		border-top-color: transparent;
		content: " ";
		margin-top: -10px;
		position: absolute;
		top: 50%;
	}
}

.reader-popover__wrapper {
	display: flex;
	flex-direction: column;
}

.reader-popover__header {
	border-bottom: 1px solid var(--color-neutral-5);
	color: var(--color-neutral-70);
	display: flex;
	font-size: $font-body-small;
	font-weight: bold;
	justify-content: flex-start;
	padding: 10px 0 10px 15px;
}