Custom CSS styles missing from Outlook

[daGUY]

Describe the bug
Custom CSS styles aren’t applied when viewing the sent email in Outlook.

To Reproduce
Steps to reproduce the behavior:

1. Follow the provided directions to implement a custom CSS stylesheet for the starter kit components: https://github.com/Kentico/xperience-by-kentico-email-builder-starter-kit/blob/main/docs/Usage-Guide.md#define-email-css-styles
2. Apply the classes defined in the above custom stylesheet via the “CSS class” field on the individual components (Button, Text, etc.) as needed

Expected behavior
The custom CSS classes should be applied in the same way that they’re shown in the email preview in Kentico (and when viewing the sent email in Gmail).

Library Version

• Email Builder Starter Kit 1.1.0
• XbyK 30.8.3

Desktop (please complete the following information):

• OS: macOS Sequoia 15.6.1
• Safari 18.6

Smartphone (please complete the following information):

• Device: iPhone 12 Pro
• OS: iOS 18.6.2
• Safari

Additional context
The custom CSS styles are preserved when viewing the same email in Gmail.