To customize the look and feel of WooCommerce mails you can use the WP HTML mail WooCommerce Extension. Without writing a single line of code you can customize colors, fonts, images …
UPDATE: WP HTML Mail for WooCommerce can customize all of your WooCommerce email text, images and product table and add even more content.
If you want to change the content, for example the text you can still override the template files.
Create WooCommerce template folder
Create a folder inside your theme or child theme your-theme/woocommerce/emails/ .
Copy WooCommerce email templates
Normally you’d copy files from the woocommerce plugin template folder, but if you use the WP HTML mail plugin you should copy the templates from plugins-folder/wp-html-mail-woocommerce/views/woocommerce/template .
I removed some inline styles from the original templates to make them more customizable.