You can customize your Invite, Announcement, and Reminder emails.  These are emails that are sent from the full event editor, Invite & Remind tab.  Also emails that are sent from the Email button in your event popups.

Login to your calendar > click Admin Menu > under Branding & Calendar colors, click Reminder Email Template

1.) Click on the Themes tab to create a new email theme.

2.) Click New and enter a name for this email theme.

3.) Use the Layout and Styles tabs to customize the Size, Colors, Text and Links in this email theme.

4.) Click the Categories tab to assign your email theme to a specific category and then save your settings

Categories Tab

Use the drop downs to select which email template theme will be used for each category

 Layout Tab

Change email size, border colors, email heading, sub heading, footer text, URL links for sub-heading and footer

 Styles Tab

Customize font size, styles, text color and alignment for the heading, body and footer of the email.

 Themes Tab

Create multiple themes of your email template to be used for different categories.