Cascading Style Sheets (CSS) is a style sheet language used to describe the presentation (that is, the look and formatting) of a document written in a markup language. wikipedia.org

HTML5 is a language for structuring and presenting content for the World Wide Web, and is a core technology of the Internet originally proposed by Opera Software. It is the fifth revision of the HTML standard. wikipedia.org

The front end is responsible for collecting input in various forms from the user and processing it to conform to a specification the back end can use. The front end is an interface between the user and the back end. wikipedia.org

Graphic design is a creative process - most often involving a client and a designer and usually completed in conjunction with producers of form (i.e., printers, signmakers, etc.) _ undertaken in order to convey a specific message (or messages) to a targeted audience. wikipedia.org

Litmus is an email campaign management and analytics platform.

Mailchimp helps you design email newsletters, share them on social networks, integrate with services you already use, and track your results. It's like your own personal publishing platform. wikipedia.org

Email marketing software that enables you to create, target, deliver, track and manage permission-based email marketing communication.

"Marketo is a Marketing Automation solution encompassing B2B marketing & lead management, Email & campaign management, Personalization across channels and marketing Budget & calendar Plan." wikipedia.org

Klaviyo is an email marketing platform.