woocommerce/plugins/woocommerce-admin/client/marketplace/components/tabs/tabs.scss

.woocommerce-marketplace__tabs {
	.woocommerce-marketplace__tab-button {
		border-bottom: 3.5px solid transparent;

		&:focus:not(:disabled) {
			box-shadow: none;
		}

		&.is-active {
			border-color: var(--wp-admin-theme-color);
		}
	}
}