This is a proof of concept, re-creating USWDS styles in MJML.
Email clients don't render everything the same way as web browsers -- for example, <button>
element is not supported in email clients. There are many workarounds to get buttons to work in many email clients, each with pros and cons.
Tools like MJML help make this easier, by providing an abstraction layer over the complex markup we need to ensure cross-email-client compatibility.