wp-calypso/client/my-sites/plans/components/upgrade-button/style.scss

.plans-upgrade-button__button {
	&.blue {
		background-color: var(--studio-blue-60);
		color: var(--studio-blue-0);
		border: unset;

		&:hover {
			background-color: var(--studio-blue-60);
			opacity: 0.85;
			transition: 0.7s;
		}
	}
}