Adding CSS to Your Brand Templates
Courier email templates use inline styles by default. You can add custom CSS in the<style> element in the <head> section of your brand; this works with both the Designer UI and custom MJML/Handlebars templates.
Brand Designer View

Custom Template View

MJML Rendering
Courier renders email templates using MJML, which compiles your template into nested HTML<table> structures. Each Courier block becomes a set of wrapper elements, so your target content is usually nested inside the CSS class rather than directly on it. Use the universal selector (*) to reach all child elements:
Test your CSS changes carefully. Create an email notification with the relevant block types and use the preview tab to verify the results.
Content Block Classes
Text Classes
Layout Classes
Example
To change the background color and font of all text blocks:Brand Designer
Customize brand logos, colors, headers, and footers
Email Safe Formatting
HTML and CSS best practices for email clients