wp-calypso/client/sites/components/sites-dashboard-header.scss

.sites-dashboard-header {
	.add-new-site__button {
		&.is-secondary {
			background-color: rgb(56, 88, 233);
			border-color: rgb(56, 88, 233);
			color: rgb(255, 255, 255);
			font-family: -apple-system, BlinkMacSystemFont, "Segoe UI", Roboto, Oxygen-Sans, Ubuntu, Cantarell, "Helvetica Neue", sans-serif;
			font-style: normal;
			font-weight: 400;
			line-height: 22px
		}

		outline: none;
		border-radius: 2px 0 0 2px;
		-moz-osx-font-smoothing: grayscale;

	}

	.components-button.is-secondary:hover {
		color: rgb(255, 255, 255);
		background-color: rgb(33, 69, 230);
	}
}