Customize customer processing email with CSS?

Hi,
I use WooCommerce Pluging and I would like to customer the style of the email sent to customers when new order is placed online. I know that I could change css style in email-style.php under my child-theme. however, I added these CSS below, they do not work. (All these CSS names were found in the email using Chrome:developer view)

CSS added to email-style.php

.x_wc-bacs-bank-details-heading{ display: none;}
.x_wc-bacs-bank-details-account-name { display: none;}
.x_wc-bacs-bank-details { display: none;}
.x_order_details { display: none;}
.x_bacs_details { display: none;}

Then, I tried to find where were these CSS defined. Very weird, they couldn’t be found anywhere in the /wp-contents/ directory!

Here are all the plugins I have used in this particular site.

WordPress Plugins Installed:
Theme: OceanWP v1.5.28 and use OceanWP-child theme
Ocean Extra v1.4.29
All in One WP Security v4.3.7.2
Contact Form 7 v5.0.4
Duplicator v1.2.48
UpdraftPlus Backup / Restore v1.15.3
User Role Editor v4.46
WP Mail SMTP v1.3.3
WordPress content import v0.6.4
WooCommerce v3.4.6
Woo Checkout Field Editor Pro 1.2.8
Loco Translate v2.1.5
Elementor v2.2.7
Woocommerce All Discounts – Dynamic pricing plugin V1.7

Can anyone help me on this?

Stonez