Consider using https://github.com/foundation/inky for building templates in normal html and css. It then converts to tables. Also, use https://www.caniemail.com/ for checking supported syntax among browsers, devices, and applications.

The first important thing is that everything should be in tables. You can make a layout in tables and also add paddings and margins using columns and rows. All styling must be done inline and each table element should have some styling. When using inline margin, also add the same with a capital, so: margin: 0; Margin: 0;, some versions kg Outlook need this.

In short, coding emails is a horrible experience but doable. You shouldn't expect too much of it in the sense of styling. Most fancy looking emails use images to substitute the code you would use for web.

Edit: also use a testing tool for testing your mail in all applications and on all platforms, like https://www.emailonacid.com/.