CSS Support | Gmail
You can style email sent to Gmail using inline <style> blocks and standard CSS. Most CSS selectors, attributes, and media-queries are supported.
CSS in HTML Email
CSS will work in HTML email but it has limitations. In general, keeping your CSS basic is always best when custom-coding an email.
Email CSS: Do's and Don'ts
An HTML email with inline CSS virtually causes no rendering issues for email clients. Now generally, inline CSS is a “bad idea” since it lacks ...
Class selector
The class selector ( .className ) allows to apply styles to a group of elements with the corresponding class attribute.
Email Template CSS Classes
Courier lets you style email templates using inline CSS and standardized class names. Customize blocks, headers, footers, and text elements.