Customize customer processing email with CSS?

Hi,
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!

Can anyone help me on this?

Stonez