Emails have different requirements compared to html pages. Not all email clients can support links to css files, so it's important to include the necessary css rules within a style tag in the head section or convert the css into inline style properties within the html elements.
If you need help with converting css into inline styles, you can use this helpful online tool:
For more information on styling emails with css, check out this informative article: https://css-tricks.com/using-css-in-html-emails-the-real-story/
It seems like you're already using inline styles, so there's no need for a CDN include. All the styling is directly applied to the elements. Could you share a snippet of your code?