woocommerce/plugins/woocommerce-admin/client/settings/style.scss

.woocommerce-admin-page__settings_page {
	.woocommerce-layout__primary {
		margin: 0;
	}
	.woocommerce-layout .woocommerce-layout__main {
		padding-right: 0;
	}
	#wpbody-content {
		background-color: white;
	}
}

.woocommerce-settings-tabs {
	.components-tab-panel__tabs {
		border-bottom: 1px solid lightgray;
		padding: 14px 14px 0 14px;
	}
	.components-tab-panel__tabs-item {
		font-weight: 400;
		border: 2px solid transparent;

		&.active-tab {
			border-bottom: 2px solid blue;
		}
	}
}