By default emails will be sent as plaintext. If you wish to change this to be HTML simply go to WPPizza -> Templates and change the format from “Plaintext” to “HTML”.

Once you have done so, the grayed out button that let’s you edit email styles will become available. Click on it to set style declarations as required.

Use the preview button to preview your settings.
Use your browsers elements inspector in the preview window to view the source and what declarations are applied where.

Do not forget to save when you are done.

Note: style declarations in emails are deliberately set to be inline per element as many email clients strip any css styles/stylesheets