Email styling options can be access by clicking on Styling under Emails menu:
By default, styling is only applied to custom emails created with this plugin. However, you can opt to change styling of default WooCommerce emails as well. Simply change the Override default WooCommerce email templates to Yes and hit Save changes. This will make sure all your emails look and feel the same.
WooCommerce Email Center comes with a powerful email style editor called Styler. This tool allows you to control all aspects of how your emails look - from background color, to footer padding and table border style. Styler is based on built-in WordPress theme customizer which provides users with familiar and easy to use interface.
To launch Styler, click on the big Launch Styler button. This will open a full screen (no admin bar and menu) user interface:
At the top left is a close button which will return you to the Styling page in admin area. Next to it are Reset and Save & Publish buttons. Clicking on Reset will reset all styling rules to default values (any changes will be lost). Saving styling has immediate effect - all emails sent after this point will use new styling.
At the right side a preview email is displayed. This is not a real email - it is based on WooCommerce Processing Order email but contains some more content so that all styling rules can be previewed live.
Styler is organized into panels and sections. Clicking on a panel name (e.g. General, Header, Footer etc.) will open a corresponding panel and clicking on section name will expand that section:
To return to a list of all panels, simply hit the "back" button at the top left corner.