The styles of the email template can be modified via the files. Depending on the layout mode (list/table), different files should be modified. Modify this file for the list mode:
Amasty/Acart/view/frontend/templates/email/list.phtml
And this file is for the table mode:
Amasty/Acart/view/frontend/templates/email/table.phtml
To set the layout mode, please navigate to Marketing → Email Templates, open the Abandoned Cart Email template, and find the layout in the Template Content field.