Rocket.Chat/app/threads/client/threads.css

.message.thread-main {
	padding-top: var(--default-padding);
	padding-bottom: var(--default-padding);

	border-bottom: 1px solid var(--color-gray-light);
}

.message.thread-message {
	padding-top: 16px;
	padding-bottom: 8px;
}

.thread-message + .thread-message {
	border-top: 1px solid var(--color-gray-light);
}

.thread-empty {
	padding: calc(2 * var(--default-padding));
}

.thread-list {
	overflow: auto;

	word-wrap: break-word;
	flex-shrink: 1;
}

.thread-replied {
	overflow: hidden;

	white-space: nowrap;
	text-overflow: ellipsis;

	color: var(--color-gray);

	font-size: 14px;
}

.message.sequential > .body > .thread-replied {
	display: none;
}

.thread-quote {
	cursor: pointer;

	color: var(--rc-color-link-active);
}

.contextual-bar__content.thread,
.contextual-bar__content.threads {
	padding: 0;
}

.js-open-thread {
	cursor: pointer;
}