Customize Elements with CSS

There are various options for global design. But if you would like to dive deeper to achieve a sophisticated design, you can consider using CSS to further customize the email elements.
For example, if you wish to change the text link color of the customer's email address and phone number, you can add this CSS snippet:
td.yaymail_billing_address_content address > span > a{
color: red !important;
Just navigate to the Settings tab, enable Custom CSS, add the CSS to the box, and click Save.
Refer to the screenshot below, I'm changing the color into green.
Likewise, you can also change many aspects like removing the underline, turning them into bold font, and so on.