Yes, it is possible to use HTML attributes or CSS styles.
See Watcher “watcher.actions.email.html.sanitization” table attributes
E.g.
<table border='1' style='font-family:sans-serif;font-size:13px'>
Just pay attention to the HTML sanitization.
Elasticsearch will filter some HTML tags or elements.
If you see some elements are not present in the final email, it means you have to allow the element in sanitization using those settings.