Cascading Style Sheets (CSS) is a feature of HTML (the standard computer language so documents can be correctly displayed by a web browser) which applies style definitions to control how the elements of a web page look!
These style definitions are written in a file, called style sheet. Multiple style sheets can be applied to the same web page, hence the term cascading in CSS.
In web development, HTML tags are used to structure a website or arrange the elements in it, while CSS is used to define what the elements will look like. Together, they allow you to design and build basic web pages. CSS allows you to achieve animations such as hover, zoom, or parallax. You can also visit our CSS wiki site for more of them in action!
Zoomforth handles the difficult parts of the designs for you, so you mostly do not have to worry about these finer details unless you're interested in theme development or animations for your sites. If you have experience with CSS or want to learn more, though, you can check related articles like the ones about adding your custom CSS to the elements of a Zoomforth site, and using CSS classes.