wp-calypso/client/components/button-group/style.scss

.button-group {
	.button {
		border-left-width: 0;
		border-radius: 0;

		&:focus {
			// fixes focus styles in stacking context
			position: relative;
			z-index: z-index("button-group-parent", ".button-group .button:focus");
		}
	}

	.button:first-child {
		border-left-width: 1px;
		border-top-left-radius: 2px;
		border-bottom-left-radius: 2px;
		&:active {
			border-right-width: 0;
		}
	}

	.button:last-child {
		border-top-right-radius: 2px;
		border-bottom-right-radius: 2px;
		&:active {
			border-left-width: 0;
		}
	}

	.section-header & .button {
		margin-right: 0;
	}

	&.is-primary {
		&.is-busy {
			background-size: 120px 100%;
			background-image: linear-gradient(-45deg, var(--color-accent) 28%, var(--color-accent-60) 28%, var(--color-accent-60) 72%, var(--color-accent) 72%);
		}
	}

	&.is-busy {
		pointer-events: none;
		animation: button__busy-animation 3000ms infinite linear;
		background-size: 120px 100%;
		background-image: linear-gradient(-45deg, var(--color-neutral-0) 28%, var(--color-surface) 28%, var(--color-surface) 72%, var(--color-neutral-0) 72%);
		display: inline-block;
		border-radius: 2px;

		.button {
			background-color: transparent;
		}
	}

}

@keyframes button__busy-animation {
	0% {
		background-position: 240px 0;
	}
}