We use the built in WooCommerce email template system. To override the email you should copy this file:
/wp-content/plugins/pw-woocommerce-gift-cards/templates/woocommerce/emails/customer-pw-gift-card.php
To here (you may need to create the subfolders if they do not exist in your theme folder):
/wp-content/themes/<your_theme>/woocommerce/emails/customer-pw-gift-card.php
Once the file is in your theme folder, open it up in a text editor and make any changes. You can change colors, wording, etc.
You can find out more about customization here: https://docs.woocommerce.com/document/configuring-woocommerce-settings/#section-21
To add a background image for the gift card, insert the “background-image” CSS tag. For example:
.pwgc-gift-card-container {
border-style: solid;
border-width: 1px;
border-color: #333;
border-radius: 16px;
background-color: #FFFEE0;
padding: 0px 24px;
background-image: url('https://yoursite.com/wp-content/uploads/bg-email-card.jpg');
}
Hope that helps, let me know if you have any questions!