joplin/packages/app-desktop/gui/styles/toolbar-button.scss

.toolbar-button {
	border: none;
	background: transparent;
	color: inherit;
	padding: 0;
	opacity: 1;
	height: var(--joplin-toolbar-height);
	min-height: var(--joplin-toolbar-height);
	width: var(--joplin-toolbar-height);
	max-width: var(--joplin-toolbar-height);

	display: flex;
	align-items: center;
	justify-content: center;
	cursor: default;
	border-radius: 3px;
	box-sizing: border-box;
	color: var(--joplin-color3);
	font-size: calc(var(--joplin-toolbar-icon-size) * 0.8);
	padding-left: 5px;
	padding-right: 5px;
	white-space: nowrap;
	overflow: hidden;
	text-overflow: ellipsis;

	> .toolbar-icon {
		font-size: 16px;
	}

	&.-has-title {
		width: auto;
		max-width: unset;
	}

	&:disabled {
		opacity: 0.3;
	}

	&:not(:disabled) {
		&:hover, &:focus-visible {
			background-color: var(--joplin-background-color-hover3);
		}
	}
}